The Corporate Executive Board Co. v. Dept. of Taxation ( 2019 )


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  • PRESENT: All the Justices
    THE CORPORATE EXECUTIVE BOARD COMPANY
    OPINION BY
    v. Record No. 171627                                JUSTICE STEPHEN R. McCULLOUGH
    February 7, 2019
    VIRGINIA DEPARTMENT OF TAXATION
    FROM THE CIRCUIT COURT OF ARLINGTON COUNTY
    Daniel S. Fiore, II, Judge
    The Corporate Executive Board Company (“CEB”) challenges its income tax assessment
    for the years 2011, 2012, and 2013. CEB contends that the method employed by the Virginia
    Department of Taxation is unconstitutional as applied to CEB under the “dormant” Commerce
    Clause and the Due Process Clause of the United States Constitution. Alternatively, CEB argues
    that it is entitled to an adjustment because the statutory method for computing its tax constitutes
    an “inequitable” method under the Tax Department’s regulations. For the reasons noted below,
    we will affirm the judgment of the circuit court.
    BACKGROUND
    I.      CEB SELLS MOST OF ITS SERVICES TO CUSTOMERS OUTSIDE OF VIRGINIA.
    CEB is a corporation that is headquartered in Arlington, Virginia. CEB describes itself as
    “the premier ‘best practices’ advisory firm in the world.” Most of CEB’s revenue comes from an
    annual fixed fee subscription service of its “Core Product.” This subscription service provides
    “online access to best practices research, executive education and networking events, and tools
    used by executives to analyze business functions and processes.” In addition, CEB sells
    professional services, or “Solutions,” that include employee education and performance
    analytics. It also conducts executive education seminars. CEB’s customers include 97% of the
    Fortune 100 companies and more than 10,000 additional organizations in more than 50 countries.
    The vast majority of CEB’s sales of its Core Product and Solutions, over 95%, occur
    outside of Virginia. The Commonwealth accounts for less than 5% of CEB’s gross revenue. For
    the three years at issue, CEB earned $1.76 billion in total sales. Of that total, Virginia accounted
    for about $66 million.
    For the tax years in question,
    [T]he majority (more than 50%) of CEB’s employees who
    developed and improved the content integrated into the online
    components of CEB’s products, and the costs of performance
    associated with developing and improving that content, were
    located in Arlington, Virginia.
    Aside from “live learning events, executive networking, and customized advisory support,” the
    entirety of the content “developed and integrated into the online components of the Core Product
    was housed on CEB’s servers located in Arlington, Virginia.” These “servers were managed
    and/or controlled by CEB’s Information Technology function located in Arlington, Virginia.”
    II.      FORMULARY APPORTIONMENT UNDER VIRGINIA LAW.
    Like a majority of States, Virginia imposes a corporate income tax. Code § 58.1-400 et
    seq. Virginia employs a formula to determine which portion of a corporation’s income it can
    properly tax.
    Because tracing income earned by an interstate business to its
    geographic origin based on some type of separate accounting
    methodology presents enormous practical problems (and is
    arguably incoherent in theory), states have long used the method of
    formulary apportionment to determine the amount of income
    earned by multistate corporations within their borders.
    Bradley W. Joondeph, The Meaning of Fair Apportionment and the Prohibition on
    Extraterritorial State Taxation, 71 Fordham L. Rev. 149, 155 (2002).
    Since 1960, Virginia has adhered to the approach recommended by the National
    Conference of Commissioners on Uniform State Laws in 1957 in a model statute. See 1960 Acts
    2
    ch. 442. 1 This model statute is the Uniform Division of Income for Tax Purposes Act, or
    UDITPA. UDITPA was drafted to address the fact that States had adopted “various formulae for
    determining the amount of income to be taxed, and the differences in the formulae produce
    inequitable results.” Uniform Division of Income for Tax Purposes Act, Prefatory Note, 3
    (1957). UDITPA sought to provide “a uniform method of division of income for tax purposes
    among the several taxing jurisdictions.” 
    Id. 2 Virginia’s
    UDITPA-based statute employs a three-factor formula to determine the taxable
    income of a corporation. Code § 58.1-408. Many States employ a similar approach. See Steven
    Maguire, Congressional Research Service, State Corporate Income Taxes: A Description and
    Analysis at 4 (2006) (hereafter “State Corporate Income Taxes”) (“Typically, three factors of
    economic activity are used in the apportionment formula to measure the economic presence of a
    firm in a state: the percentage of property, the percentage of sales, and the percentage of
    payroll.”). In Virginia, the numerator of the fraction consists of three factors: a payroll factor, a
    property factor, and a double-weighted sales factor. Code § 58.1-408. The denominator is four.
    
    Id. “In practice,
    there is relatively little controversy surrounding the [property and payroll
    factors].” Walter Hellerstein, State Taxation of Electronic Commerce, 52 Tax L. Rev. 425, 476
    (1997).
    1
    In 1999, Virginia adopted a double-weighted sales factor. 1999 Acts chs. 158, 186.
    2
    The Multistate Tax Compact, a model law drafted in 1966 by a group of State officials,
    incorporates UDITPA nearly verbatim in Article IV of that Compact. Some States adopted
    UDITPA directly into their statutes, while other States enacted the Multistate Tax Compact.
    Shirley Sicilian, Multistate Tax Compact Article IV Recommended Amendments 1-2 (May 3,
    2012).
    3
    The sales factor is based on the ratio of a corporation’s “sales . . . in the Commonwealth”
    to its total “sales . . . everywhere.” Code § 58.1-414. The sales factor varies depending on
    whether the property is tangible or intangible. For tangible personal property, Virginia’s sales
    factor attributes the income from the sale to the source of the revenue, i.e. where the customer is
    located. Code § 58.1-415. This approach, modeled on UDITPA § 16, is known as
    destination-based, or market-based, sourcing. Virginia modeled the sales factor for sales of
    intangible personal property, including services like CEB’s Core Product, on UDITPA § 17.
    Virginia includes sales of intangible property as part of income if:
    1. The income-producing activity is performed in the
    Commonwealth; or
    2. The income-producing activity is performed both in and outside
    the Commonwealth and a greater portion of the income-producing
    activity is performed in the Commonwealth than in any other state,
    based on costs of performance.
    Code § 58.1-416. 3 Aside from minor textual adjustments and recodification, Virginia has
    retained this sales factor for services for nearly 60 years. See 1960 Acts ch. 442.
    Applying this long-accepted “costs of performance” formula for sales of services means
    that the Tax Department allocated nearly 100% of CEB’s gross receipts to Virginia. This
    allocation occurred because the service CEB provides was developed in Virginia by CEB’s
    Virginia employees, and its product is stored on servers located in Virginia.
    3
    Code § 58.1-416 was amended in 2018, by adding three new subsections, (B), (C), and
    (D), and placing the language from the previous version of the statute under a new subsection
    (A). See 2018 Acts ch. 807. The amendments did not change the relevant language. We cite to
    the version of the statute in effect during the tax years in question.
    4
    III.   OTHER STATES ABANDON “COST OF PERFORMANCE” SOURCING.
    UDITPA’s, and, therefore, Virginia’s, “costs of performance” sales factor has faced
    mounting criticism. See, e.g., John A. Swain, Reforming the State Corporate Income Tax: A
    Market State Approach to the Sourcing of Service Receipts, 83 Tul. L. Rev. 285, 289 (2008).
    UDITPA was adopted in 1957. It “was written against the backdrop of an economy dominated
    by mercantile and manufacturing enterprises.” 
    Id. at 287.
    The U.S. economy, however, has changed dramatically since that
    time. Production has shifted steadily from goods to services and
    intangibles, and the forces of globalization, spurred by the
    revolution in communications technology, now allow many more
    goods and services to be supplied remotely. This puts tremendous
    pressure on division of income rules that were developed in
    another era.
    
    Id. 4 Virginia
    has repeatedly studied whether to alter its apportionment formula for services,
    but, to date, the General Assembly has not changed it. See John P. Josephs, Jr., Virginia’s
    Apportionment Formula, Presented to the Joint Subcommittee Studying the Benefits of Adopting
    a Single Sales Factor (September 30, 2008); Joint Legislative Audit and Review Commission,
    Report to the Governor and the General Assembly of Virginia, Review of Virginia’s Corporate
    Income Tax System (November 2010). Several bills have been introduced to that effect, but they
    have not passed. See H.B. 1604, Va. Gen. Assem. (Reg. Sess. 2011), S.B. 1006, Va. Gen.
    4
    “In 1960, 42 percent of U.S. wages and salaries were earned in the goods-producing
    sector (manufacturing, mining, construction, and agriculture)” of the economy. In 2000, the
    share had fallen to 24%. The portion of personal consumption dollars spent on services rose
    during this same period from 41% to 58%. Robert Tannenwald, Are State and Local Revenue
    Systems Becoming Obsolete?, 24 State Tax Notes 143, 146 (2002).
    5
    Assem. (Reg. Sess. 2011), H.B. 2253, Va. Gen. Assem. (Reg. Sess. 2013), H.B. 442, Va. Gen.
    Assem. (Reg. Sess. 2014).
    A growing number of States have revisited their method of apportioning income from the
    sale of services. “The cost-of-performance method is waning, and market sourcing is taking its
    place.” Douglas A. Wick, A Categorization of State Market Sourcing Rules, 74 State Tax Notes
    351 (2014).
    [I]n recent years states have been moving away from the traditional
    cost-of-performance approach for sourcing revenue from services
    and adopting a market-based sourcing approach. Under this
    approach, service receipts are sourced to the location of the
    customer that receives the benefit of the service, rather than to the
    state where the service is performed.
    Chuck Jones, et al., Addressing the Impact of Trend in States to Source Financial Services Fee
    Income by Using Market-Based Approach, 23 J. Tax’n F. Inst. 29, at *3 (Nov./Dec. 2009). 5
    As States revise their apportionment formulas, however, they are not doing so in a
    uniform manner. Some States tax services where the benefit is received, others where the
    service is delivered, and still others where the receipts are derived. See Wick, 74 State Tax
    Notes 351, at *4-6; see also Sicilian, supra note 2, at 19-20. Still other States have modified
    5
    In 2006, the National Conference of Commissioners on Uniform State Laws proposed a
    study to review UDITPA for possible revisions. In response, in 2012, the Multistate Tax
    Commission (“Commission”) recommended a number of changes to UDITPA, and in particular
    to the apportionment formula for services. Sicilian, Multistate Tax Compact Article IV
    Recommended Amendments at 18-24. In July 2015, the Commission voted to adopt the Revised
    Model Compact Article IV, which addresses the apportionment of income. See Brian Hamer,
    Hearing Officer Report, Synopsis and Recommendations on Proposed Draft Amendments to the
    Commission’s Model General Allocation and Apportionment Regulations 6 (May 1, 2016),
    http://www.mtc.gov/Uniformity/Project-Teams/Section-17-Model-Market-Sourcing-Regulations
    (last visited November 26, 2018). On February 24, 2017, the Commission voted to adopt draft
    amendments to the Commission’s Model General Allocation and Apportionment Regulations.
    See 
    id. 6 their
    apportionment rules for specific industries. 
    Id. at 20.
    These divergent approaches on the
    sales factor expose corporations to potential or actual multiple taxation.
    According to the parties’ stipulation, approximately one third of the States where CEB
    does business use the same “‘costs of performance’ sales factor sourcing rule used by Virginia.”
    A number of other States, however, included the income from CEB sales in their sales factor. As
    a result of this overlap between other States’ apportionment formulas and Virginia’s formula,
    CEB has “paid tax on a multistate basis on an apportioned amount of income that exceeded 120
    percent of CEB’s nationwide income.” For example, according to the parties’ stipulation, for the
    year 2013,
    CEB assigned 9.6 percent of its sales (or just over $65 million of
    revenue) to California to reflect its customer base there, and CEB
    also assigned these sales to the Commonwealth under the Statutory
    Method. Thus, CEB’s taxes in Virginia and California were based
    in part on the same $65 million of revenue from customers located
    in California.
    IV.     THE RELIEF PROVISION.
    The Code contains a relief provision that allows a taxpayer to seek redress from the Tax
    Department when “the method of allocation or apportionment hereinbefore prescribed . . . has
    operated or will so operate as to subject [a corporation] to taxation on a greater portion of its
    Virginia taxable income than is reasonably attributable to business or sources within this
    Commonwealth.” Code § 58.1-421. A corporation seeking the benefit of this provision must file
    “a statement of its objections” with the Tax Department and propose an “alternative method [of
    taxation] as it believes to be proper under the circumstances.” 
    Id. If the
    Tax Department
    “concludes that the method of allocation or apportionment theretofore employed is in fact
    inapplicable or inequitable,” then “it shall redetermine the taxable income by such other method
    of allocation or apportionment as seems best calculated to assign to the Commonwealth for
    7
    taxation the portion of the income reasonably attributable to business and sources within the
    Commonwealth.” 
    Id. The Tax
    Commissioner has issued a regulation, 23 VAC § 10-120-280, that specifies
    when a method of allocation and apportionment is inapplicable or inequitable. This regulation
    specifies that a method will be found “inapplicable” only if it “produces an unconstitutional
    result under the particular facts and circumstances of the taxpayer’s situation.” 23 VAC
    § 10-120-280(B)(4)(a). A method is “inequitable” only if “[i]t results in double taxation of the
    income, or a class of income” and “[t]he inequity is attributable to Virginia, rather than to the
    fact that some other state has a unique method of allocation and apportionment.” 23 VAC
    §§ 10-120-280(B)(4)(b)(1) and (2).
    V.      THE PROCEEDINGS BELOW.
    CEB sought an administrative refund from the Tax Department under Code § 58.1-1823,
    and asked for apportionment relief under Code § 58.1-421. The Tax Department did not act
    within three months after the refund claim was filed, thereby allowing CEB to seek relief in
    court. See Code § 58.1-1823. It did so, filing a complaint in the Arlington County Circuit Court
    in 2016. As relevant here, the complaint alleged that the assessments violated the Commerce
    Clause and the Due Process Clause of the United States Constitution. In addition, CEB alleged
    that the assessments were “inequitable” under Code § 58.1-421 and 23 VAC § 10-120-280. CEB
    requested a redetermination of its income tax by using the customer’s location, the same formula
    as is employed for sales of tangible personal property, to allocate sales. Under its proposed
    method, sales would be sourced to the billing address of the customer instead of to Virginia
    based on the cost of performance. The parties submitted a joint motion for summary judgment
    8
    on stipulated facts. The circuit court found in favor of the Tax Department. This appeal
    followed.
    ANALYSIS
    I.      THE TAX DEPARTMENT’S APPORTIONMENT OF CEB’S INCOME TAX IS IN ACCORD
    WITH CONSTITUTIONAL REQUIREMENTS.
    CEB argues that the Tax Department unconstitutionally apportioned its income in 2011,
    2012, and 2013, in violation of the “dormant” Commerce Clause and the Due Process Clause of
    the Fourteenth Amendment. We review de novo the legal question of whether a statute has been
    constitutionally applied by a governmental agency. Dulles Duty Free, LLC v. Cnty. of Loudoun,
    
    294 Va. 9
    , 13 (2017).
    The Due Process Clause of the Fourteenth Amendment provides that “[n]o . . . State shall
    deprive any person of life, liberty, or property, without due process of law.” U.S. Const. amend
    XIV, § 1. “For a State to tax income generated in interstate commerce, the Due Process Clause
    of the Fourteenth Amendment imposes two requirements: a ‘minimal connection’ between the
    interstate activities and the taxing State, and a rational relationship between the income attributed
    to the State and the intrastate values of the enterprise.” Mobil Oil Corp. v. Comm’r of Taxes of
    Vt., 
    445 U.S. 425
    , 436-37 (1980).
    The Commerce Clause provides that “The Congress shall have Power . . . [t]o regulate
    Commerce with foreign Nations, and among the several States, and with the Indian Tribes.”
    U.S. Const. art. I, § 8, cl. 3. “Although the Constitution contains language explicitly limiting
    state interference with foreign commerce, nowhere does it explicitly limit state interference with
    interstate commerce.” 1 Laurence H. Tribe, American Constitutional Law 1029 (3rd ed. 2000)
    (emphasis in original). The Supreme Court’s doctrine in this area is “traceable to the
    Constitution’s negative implications.” 
    Id. (emphasis in
    original). “Although the language of
    9
    th[e] Clause speaks only of Congress’ power over commerce, the Court long has recognized that
    it also limits the power of the States to erect barriers against interstate trade.” Dennis v. Higgins,
    
    498 U.S. 439
    , 446 (1991) (internal quotation marks and citation omitted). The Court has
    conceived of the Commerce Clause as not only “an affirmative grant of power to Congress to
    regulate interstate and foreign commerce” but also as a “self-executing limitation on the power
    of the States to enact laws imposing substantial burdens on [interstate] commerce.”
    South-Central Timber Dev., Inc. v. Wunnicke, 
    467 U.S. 82
    , 87 (1984).
    “The Commerce Clause . . . precludes the application of a state statute to commerce that
    takes place wholly outside of the State’s borders, whether or not the commerce has effects within
    the State.” Edgar v. MITE Corp., 
    457 U.S. 624
    , 642-43 (1982) (plurality opinion). A State may
    not “tax value earned outside [of] its borders,” Container Corp. of Am. v. Franchise Tax Bd., 
    463 U.S. 159
    , 164 (1983), and is limited to taxing “only its fair share of an interstate transaction.”
    Goldberg v. Sweet, 
    488 U.S. 252
    , 261 (1989).
    A tax does not infringe the dormant Commerce Clause if it:
    (1) applies to an activity with a substantial nexus to the taxing state;
    (2) is fairly apportioned;
    (3) does not discriminate against interstate commerce; and
    (4) is fairly related to services or benefits provided by the state.
    Complete Auto Transit, Inc. v. Brady, 
    430 U.S. 274
    , 279 (1977). In this case, there is no dispute
    that the tax here satisfies parts (1), (3), and (4) of the Complete Auto test. The crux of the
    disagreement between the parties is whether the tax is fairly apportioned. CEB notes that “[b]oth
    the Commerce and Due Process Clauses require a state income tax to be fairly apportioned” and
    that the “fair apportionment analysis is substantially the same under the Commerce and Due
    10
    Process Clauses.” CEB Br. 23 n.10. We agree and proceed accordingly. See Container 
    Corp., 463 U.S. at 169
    (setting forth the same test for a fair apportionment formula under both the Due
    Process Clause and the Commerce Clause).
    “[T]he central purpose behind the apportionment requirement is to ensure that each State
    taxes only its fair share of an interstate transaction.” 
    Goldberg, 488 U.S. at 260-61
    . To be fairly
    apportioned, a tax must be both internally and externally consistent. 
    Id. The parties
    agree that
    Virginia’s method of assessing CEB’s corporate income is internally consistent. The remaining
    question, therefore, is whether the tax is externally consistent.
    Of the two, the external consistency requirement is the “more difficult.” Container
    
    Corp., 463 U.S. at 169
    . “[T]he external consistency test is essentially a practical
    inquiry.” 
    Goldberg, 488 U.S. at 264
    . To be constitutionally fair, “the factor or factors used in
    the apportionment formula must actually reflect a reasonable sense of how income is generated.”
    Container 
    Corp., 463 U.S. at 169
    . “External consistency . . . looks . . . to the economic
    justification for the State’s claim upon the value taxed, to discover whether a State’s tax reaches
    beyond that portion of value that is fairly attributable to economic activity within the taxing
    State.” Oklahoma Tax Comm’n v. Jefferson Lines, Inc., 
    514 U.S. 175
    , 185 (1995); see also
    
    Goldberg, 488 U.S. at 262
    (“The external consistency test asks whether the State has taxed only
    that portion of the revenues from the interstate activity which reasonably reflects the in-state
    component of the activity being taxed.”). A court must strike down an apportionment formula as
    externally inconsistent if the taxpayer proves by “clear and cogent” evidence “that the income
    attributed to the State is in fact out of all appropriate proportion to the business transacted . . . in
    that state, or has led to a grossly distorted result.” Moorman Mfg. Co. v. Bair, 
    437 U.S. 267
    , 274
    (1978) (citation omitted).
    11
    The Supreme Court has recognized that the existence of duplicative taxation does not, by
    itself, violate the Constitution. The Court has noted that “some risk of duplicative taxation exists
    whenever the States in which a corporation does business do not follow identical rules for the
    division of income.” 
    Id. at 278.
    The Court has so far declined to undertake “extensive judicial
    lawmaking” that would be required to “prohibit[] any overlap in the computation of taxable
    income by the States.” Id.; see also Container 
    Corp., 463 U.S. at 171
    (declining to undertake the
    “essentially legislative” task of establishing a “single constitutionally mandated method of
    taxation.”). So long as the State’s method of apportionment is itself fair, it does not violate the
    Constitution. 6 Moorman 
    Mfg., 437 U.S. at 280-81
    ; see also Comptroller of the Treasury v.
    Wynne, 575 U.S. ___, 
    135 S. Ct. 1787
    , 1804 (2015) (characterizing Moorman as “distinguishing
    ‘the potential consequences of the use of different formulas by the two States,’ which is not
    prohibited by the Commerce Clause, from discrimination that ‘inhere[s] in either State’s
    formula,’ which is prohibited”).
    In a union comprised of 50 sovereign States, it is nearly inevitable that States will devise
    differing taxation schemes and, indeed, that is the case. See Maguire, State Corporate Income
    Taxes, at 6 (listing various apportionment schemes). The Supreme Court has given States “wide
    latitude” in adopting apportionment formulas, Moorman 
    Mfg., 437 U.S. at 274
    , upholding, for
    example, both single property factor apportionment, Underwood Typewriter Co. v. Chamberlain,
    
    254 U.S. 113
    , 120-21 (1920), and single sales factor apportionment. Moorman 
    Mfg., 437 U.S. at 275
    . Some States, like Virginia, have adhered to longstanding apportionment formulas while
    6
    Similarly, with respect to the internal consistency test, not at issue here, the Court has
    drawn a “critical distinction” between “discriminatory tax schemes,” which are constitutionally
    problematic under the dormant Commerce Clause, and “double taxation that results only from
    the interaction of two different but nondiscriminatory tax schemes.” Comptroller of the Treasury
    v. Wynne, 575 U.S. ___, 
    135 S. Ct. 1787
    , 1804 (2015).
    12
    others, in an effort to attract corporate investment, have adopted formulas that eliminate the
    property and payroll factors. See Swain, 83 Tul. L. Rev. 285, at 289-90. “[T]he variability in the
    allocation and apportionment of corporate income from state to state” inescapably creates “gaps
    and overlaps in taxation.” Maguire, State Corporate Income Taxes, at 16. Some income will
    escape taxation altogether, a phenomenon known as “nowhere income.” 
    Id. at 5.
    At times,
    however, as occurred here, differing apportionment formulas will result in double taxation of the
    same income. Moorman 
    Mfg., 437 U.S. at 278
    .
    We conclude that CEB did not suffer from an unconstitutional apportionment of its
    income. We can find nothing in the precedent of the United States Supreme Court interpreting
    the dormant Commerce Clause or the Due Process Clause that requires one of two taxing States
    to “recede simply because both have lawful tax regimes reaching the same income.” 
    Wynne, 135 S. Ct. at 1813
    (Ginsburg, J., dissenting). The external consistency test “asks whether the State
    has taxed only that portion of the revenues from the interstate activity which reasonably reflects
    the in-state component of the activity being taxed.” 
    Goldberg, 488 U.S. at 262
    . In the present
    case, the stipulated facts establish that the content for CEB’s Core Product was developed by
    CEB employees working in Virginia. The servers on which the product resides are located in
    Virginia. Each time a customer uses CEB’s Core Product, the customer reaches into Virginia to
    consult materials developed in Virginia and stored in Virginia. The Tax Department’s
    apportionment of income did not “reach[] beyond that portion of value that is fairly attributable
    to economic activity within the taxing State.” Jefferson 
    Lines, 514 U.S. at 185
    . “[T]he central
    purpose [of apportionment] is to ensure that each State taxes only its fair share of an interstate
    transaction.” 
    Id. at 184
    (quoting 
    Goldberg, 488 U.S. at 260-61
    ). Virginia’s apportionment
    method satisfies the constitutional standard.
    13
    CEB acknowledges that double taxation, by itself, does not render an unconstitutional
    result. It argues, however, that an apportionment is unconstitutional when it “wholly disregards
    the existence of interstate commerce, and that thereby produces a much higher apportionment of
    taxable income and substantial double taxation.” CEB Reply Br. at 4. (emphasis in original).
    Whatever the policy merits of this proposal may be, it is not a standard the Supreme Court has
    embraced. Virginia’s apportionment method for taxing sales of services satisfies the
    requirements of existing precedent from the Supreme Court. As noted above, Virginia’s taxation
    scheme “reasonably reflects the in-state component of the activity being taxed” - nothing more is
    required. 
    Goldberg, 488 U.S. at 262
    .
    Our conclusion is consistent with Western Live Stock v. Bureau of Revenue, 
    303 U.S. 250
    (1938). Although the decision predates the four-factor Complete Auto test, the Court has never
    questioned or overruled the case. New Mexico imposed a gross receipts tax on advertising
    revenues for a magazine distributed within and without the State. The magazine, a livestock
    trade journal, was wholly prepared, edited, and published within New Mexico. The taxpayer’s
    only office and place of business was located in New Mexico. 
    Id. at 252.
    The magazine
    solicited advertisements outside New Mexico. 
    Id. at 252-53.
    It received payments in its offices
    in New Mexico. 
    Id. at 253.
    The Supreme Court upheld the tax against a challenge that it
    imposed an unconstitutional burden on interstate commerce. The Court observed that “[a]ll the
    events upon which the tax is conditioned – the preparation, printing and publication of the
    advertising matter, and the receipt of the sums paid for it – occur in New Mexico and not
    elsewhere.” 
    Id. at 260.
    Finally, we conclude that Virginia’s apportionment formula does not create a “grossly
    distorted” result. In Norfolk & W. Ry. v. Missouri State Tax Commission, 
    390 U.S. 317
    , 326
    14
    (1968), the Supreme Court concluded that the taxpayer had met its “heavy burden” of proving
    that Missouri’s ad valorem tax assessment of the railway’s rolling stock violated the Due Process
    and Commerce Clauses. The railway established that the value of its rolling stock in the State
    never materially exceeded $7,600,000. 
    Id. at 321-22.
    The State’s formula, which assumed “an
    enhanced value [to the rolling stock] in the State through its organic relation to the [interstate]
    system,” yielded an assessed value of $19,981,000. 
    Id. at 322.
    The Court found that the tax
    challengers had borne the burden of showing that the State’s method “has resulted in such gross
    overreaching, beyond the values represented by the intrastate assets purported to be taxed, as to
    violate the Due Process and Commerce Clauses of the Constitution,” while “the State has made
    no effort to offset the convincing case that they have made.” 
    Id. at 326.
    Of significance to the
    Court was the fact that the State “made no effort to show such value [to the interstate system] or
    to measure the extent to which it might be attributed to the rolling stock in the State.” 
    Id. at 328.
    In the present case, by contrast, the facts establish that the tax imposed on CEB’s services rests
    upon the labor of employees in Virginia who developed the product CEB sells, which is located
    in servers stored in Virginia. The gross distortion and lopsided factual record present in Norfolk
    & Western Railway v. Missouri State Tax Commission are simply not present in this case.
    II.     THE REGULATION ALLOWING RELIEF DOES NOT APPLY UNDER ITS PLAIN LANGUAGE.
    A taxpayer is entitled to relief under Code § 58.1-421 if the statutory “method of
    allocation or apportionment” is “inequitable.” The Tax Department’s implementing regulation,
    23 VAC § 10-120-280(B)(4)(b), provides that the statutory method is “inequitable” when “(1) it
    results in double taxation of the income, or a class of income, of the taxpayer; and (2) the
    inequity is attributable to Virginia, rather than to the fact that some other state has a unique
    method of allocation and apportionment.” CEB argues in its second assignment of error that it is
    15
    entitled to benefit from this relief provision because the statutory method results in inequitable
    apportionment of its income.
    The taxpayer bears the burden of proving that the Tax Department’s assessment is
    contrary to law. Dep’t of Taxation v. Lucky Stores, Inc., 
    217 Va. 121
    , 127 (1976). Where a
    regulation is unambiguous, we will interpret it according to its plain language. Mathews v. PHH
    Mortg. Corp., 
    283 Va. 723
    , 738 (2012); see also Avante at Roanoke v. Finnerty, 
    56 Va. App. 190
    , 201-02 (2010). There is no question that the statutory method, when applied alongside the
    apportionment methods employed by a number of other States, has resulted in the double
    taxation of a portion of CEB’s income. Therefore, CEB satisfies the first requirement of the
    regulation.
    The second requirement contains two criteria: the Taxpayer must show both that the
    inequitable apportionment is “attributable to Virginia,” and that it is not attributable “to the fact
    that some other state has a unique method of allocation and apportionment.” 23 VAC
    § 10-120-280(B)(4)(b).
    For the first criterion, the key term is “attributable.” In Nielsen Co. (US), LLC v. County
    Board of Arlington County, 
    289 Va. 79
    , 94 (2015), we gave this undefined term its “ordinary
    meaning, in light of the context in which it is used,” and reasoned that “[a]ttribute,” when used as
    a verb, has the ordinary meaning of “to explain as caused or brought about by” and “regard as
    occurring in consequence of or on account of.” 
    Id. (citing Webster’s
    Third New International
    Dictionary 142 (1993)).
    Applying this definition, our overview of the history of UDITPA and States’ efforts to
    reform their apportionment rules makes it clear that any double taxation is not “attributable” to
    Virginia. CEB’s double taxation is “attributable” to changes adopted more recently by other
    16
    States in their apportionment formulas, and in particular to the increased trend of using
    single-factor sales apportionment. Virginia adopted its apportionment formula, modeled after
    UDITPA, as part of an effort to provide “a uniform method of division of income for tax
    purposes among the several taxing jurisdictions.” Uniform Division of Income for Tax Purposes
    Act, Prefatory Note at 3. The Commonwealth has adhered to its formula for nearly 60 years.
    CEB’s double taxation did not “occur[] in consequence of or on account of” Virginia law.
    For the second criterion, the key term is “unique.” Under the plain language of the
    regulation, CEB is not entitled to relief unless it can show that the double taxation is not
    attributable to “another state’s unique method of allocation and apportionment.” 23 VAC
    § 10-120-280(B)(4)(b). Determining whether a State has adopted “a unique method of allocation
    and apportionment” requires more than considering whether, at a high level of abstraction, a
    State has adopted a cost of production versus a market sourcing formula. A “method” is “a
    procedure or process for attaining an object.” Webster’s Third New International Dictionary
    1422 (1993). “Cost of production” or “market sourcing” are broad descriptive labels, useful to
    be sure, but such labels do not constitute the specific “method of allocation and apportionment”
    for assessing a corporation’s income tax. Under 23 VAC § 10-120-280(B)(4)(b), we must
    examine the specific details of another State’s “method of allocation and apportionment” to
    determine whether it is “unique.”
    The record fails to establish whether the sourcing methods adopted by other States are
    “unique.” It does not appear that an entity such as the National Conference of Commissioners on
    Uniform State Laws has developed these formulas for adoption by the States. Rather, an
    examination of the apportionment formulas themselves, and their treatment in academic
    17
    literature, indicates that each State has generated a statute that is unique to that particular State
    and, not infrequently, additional voluminous and complex implementing regulations.
    While many States have adopted sourcing methods that can be described as market based,
    these methods are far from uniform and often differ substantially. Broadly speaking, States that
    have shifted to market sourcing have adopted three approaches, with some taxing services where
    the benefit is received, others where the service is delivered, and still others where the receipts
    are derived. See Wick, 74 State Tax Notes 351, at *4-6. Even within these three approaches, the
    specifics of each method vary significantly.
    Several examples illustrate the point. Both Wisconsin and California employ the
    “benefits received” approach. In its sales factor, California includes sales of services “to the
    extent the purchaser of the service received the benefit of the services in [California].” West’s
    Ann. Cal. Rev. & T. Code § 25136(a)(1). Extensive regulations provide further guidance. These
    regulations “anticipate that determining the location where the benefit of a service is received
    can be difficult,” and provide a complex framework to aid in the determination. See Wick, 74
    State Tax Notes 351, at *5. The regulations draw a distinction between services provided to an
    individual and services provided to a business. Cal. Code Regs. tit. 18, §§ 25136-2(c)(1) and (2).
    The regulations specify that the “[b]enefit of a service is received” in “the location where the
    taxpayer’s customer has either directly or indirectly received value from delivery of that
    service.” Cal. Code Regs. tit. 18, § 25136-2(b)(1). If the contract or the taxpayer’s books and
    records indicate that the benefit was received in California, the regulations presume that the
    benefit is received in California - regardless of the customer’s billing address. Cal. Code Regs.
    tit. 18, § 25136-2(c)(2)(A). A taxpayer can overcome that presumption by showing, based on a
    preponderance of the evidence, that the location (or locations) indicated by the contract or the
    18
    taxpayer’s books and records was not the actual location where the benefit of the service was
    received. 
    Id. If the
    contract or the taxpayer’s books and records do not indicate where the
    benefit was received, the location must be reasonably approximated. Cal. Code Regs. tit. 18,
    § 25136-2(c)(2)(B). If the location where the benefit of the service is received cannot be
    determined and reasonable approximation is not possible, the location where the benefit was
    received is presumed to be in California if “the location from which the taxpayer’s customer
    placed the order for the service is in this state.” Cal. Code Regs. tit. 18, § 25136-2(c)(2)(C). If
    none of the previously stated tests apply, California law will deem the benefit of the service to be
    in California if the customer’s billing address is in California. Cal. Code Regs. tit. 18,
    § 25136-2(c)(2)(D).
    For Wisconsin, which adopted single factor sales apportionment beginning in 2008,
    receipts from services are Wisconsin receipts “if the purchaser of the service received the benefit
    of the service in this state.” Wis. Stat. Ann. § 71.25(9)(dh)(1). The benefit of a service is
    received in the State if
    a. The service relates to real property that is located in this
    state.
    b. The service relates to tangible personal property that is
    delivered directly or indirectly to customers in this state.
    c. The service is purchased by an individual who is
    physically present in this state at the time that the service is
    received.
    d. The service is provided to a person engaged in a trade or
    business in this state and relates to that person’s business in this
    state.
    3.      Except as provided in subd. 4. if the purchaser of a service
    receives the benefit of a service in more than one state, the gross
    receipts from the performance of the service are included in the
    numerator of the sales factor according to the portion of the service
    received in this state.
    19
    
    Id. at (dh)(2).
    Unlike California, the implementing regulation provides no additional guidance.
    See Wis. Admin. Code, Tax § 2.39(6)(f). Wisconsin does not provide alternative domicile,
    customer address, or billing address rules.
    Other States, including Alabama and Illinois, use the “services delivered” approach to
    market based sourcing. Alabama employs a three factor assessment formula that includes
    property, payroll, and double weighted sales factors. Ala. Code Ann. § 40-27-1, art. IV(9).
    Sales means “all gross receipts of the taxpayer not allocated under paragraphs of this article.”
    Ala. Code Ann. § 40-27-1, art. IV(1)(g). Sales are considered to take place in Alabama “if and
    to the extent the service is delivered to a location in this state.” Ala. Code Ann. § 40-27-1, art.
    IV(17)(a)(3). Implementing regulations draw a distinction between sales to an individual and
    sales to a business enterprise. Ala. Admin. Code R. 810-27-1-.17. If a sale is to a business
    enterprise, the regulations draw a further distinction between a service with a “substantial
    connection to a specific geographic location,” such as training or cleaning services, and services
    that do “not have a substantial connection to a specific geographic location,” such as providing
    accounting services. Compare Ala. Admin. Code R. 810-27-1-.17(2)(b)(2), with Ala. Admin.
    Code R. 810-27-1-.17(2)(b)(3). If the service has a “substantial connection to a specific
    geographic location,” then “the income shall be sourced to Alabama if the geographic location is
    in this state.” Ala. Admin. Code R. 810-27-1-.17(2)(b)(2). If the service provided “does not
    have a substantial connection to a specific geographic location,” the sale should be sourced to
    Alabama if the business is “commercially domiciled in Alabama.” Ala. Admin. Code R. 810-27-
    1-.17(2)(b)(3). A business is domiciled in Alabama “if its principal place of business is in
    Alabama.” 
    Id. 20 Unlike
    Alabama’s traditional three factor formula, Illinois employs a single factor sales
    formula. 35 Ill. Comp. Stat. Ann. § 5/304(a)(3)(C-5)(iv). Receipts from services provided to a
    business may be sourced only to a state where that business has a fixed place of business. 
    Id. If the
    State where the services were delivered is not readily determinable, proxies such as the
    location of the customer’s ordering office or billing address are used to determine where the
    service was received. See 
    id. Regulations provide
    additional details concerning these sourcing
    rules. See Ill. Admin. Code tit. 86, § 100.3370 (2017).
    CEB paid corporate income taxes on a portion of its sales to 23 States besides Virginia,
    including the four States mentioned above. CEB contends that “[t]he destination-based sourcing
    method used by these 23 other states . . . can in no sense be considered unique.” CEB Br. at 35.
    Cursory investigation reveals, however, that each State has adopted its own distinctive method,
    even if those methods share some conceptual similarities.
    Today, there is no standard market sourcing rule akin to the
    cost-of-performance rule that used to be more prevalent. Instead,
    three categories of market sourcing rules exist: the
    benefits-received approach, the services-delivered approach, and
    the receipts-derived approach. And as demonstrated above, in
    each state, subtle differences in those approaches may exist.
    Wick, 74 State Tax Notes 351, at *7. The fact that States have adopted, in conceptual terms, a
    market sourcing method does not resolve whether the actual method employed is “unique.”
    The taxpayer bears the burden of proving that the Tax Department’s assessment is
    contrary to law. Lucky Stores, 
    Inc., 217 Va. at 127
    . The applicable regulation, 23 VAC
    § 10-120-280(B)(4)(b), forecloses relief if the “method” employed by another State is “unique.”
    Our review of some of the methods employed by States that have taxed CEB’s sales of services,
    illustrated above, suggests that the market sourcing methods employed by States for taxing the
    sale of a service differ in their details, often considerably. In short, the record establishes that a
    21
    number of States that subject CEB to corporate income tax use conceptually similar market
    sourcing methods, but the record fails to establish whether those methods are unique.
    Consequently, we are unable to conclude that the circuit court and the Tax Department erred in
    declining to grant relief under the plain language of 23 VAC § 10-120-280(B)(4)(b). 7
    CONCLUSION
    For these reasons, we will affirm the judgment of the circuit court.
    Affirmed.
    7
    Our resolution of the first two assignments of error obviates the need for us to address
    CEB’s remaining assignment of error, which challenged the trial court’s determination that the
    Tax Department was not required to implement CEB’s proposed alternative method of
    apportionment.
    22