[218]*218VAN HOOMISSEN, J.
In this direct appeal from the Oregon Tax Court, ORS 305.445, taxpayer challenges ajudgment that denied her claim for a refund of state income taxes paid on her federal retirement benefits for the tax year 1991. Ragsdale v. Dept. of Rev., 13 OTR 143 (1994). She claims that Oregon discriminates in taxation between state and federal retirees in violation of the federal constitutional and statutory doctrine of intergovernmental tax immunity.1 This court reviews de novo. ORS 305.445; 19.125(3). For the reasons that follow, we affirm the judgment of the Tax Court.
At all times relevant to this appeal, retired public employees of the State of Oregon and of its political subdivisions and instrumentalities have received retirement benefits attributable to their employment under the Public Employes’ Retirement System (PERS).2 See ORS chapter 237 (Public Employes’ Retirement). Before 1991, ORS 237.201 (1989) provided that PERS retirement benefits were exempt from all state taxes.3 Further, ORS 316.680(l)(d) (1989) excluded PERS retirement benefits from the taxable income base on which state income taxes were computed. There was no comparable statutory provision exempting federal retirement [219]*219benefits from state taxes. As a result, Oregon taxed federal retirement benefits, but not PERS retirement benefits.4
In 1989, the Supreme Court of the United States decided Davis v. Michigan Dept. of Treasury, 489 US 803, 817, 109 S Ct 1500, 103 L Ed 2d 891 (1989). At issue in Davis was whether a Michigan statute that fully taxed all federal retirement benefits, but excluded from taxable income all retirement benefits received from the State of Michigan or its political subdivisions, violated the principle of intergovernmental tax immunity by favoring retired state and local government employees over retired federal employees based on the source of the benefits.5
In Davis, the Supreme Court held that, if a state exempts retirement benefits paid by state and local governments from state income taxes without similarly exempting retirement benefits paid by the federal government from state income taxes, then that state violates the principle of intergovernmental tax immunity. Davis, 489 US at 810-17. That is to say, a state may not discriminate in taxation between state and federal retirement benefits, based on the source of the benefits.6 The Supreme Court stated: “It is undisputed that Michigan’s tax system discriminates in favor of retired state employees and against retired federal employees.” Id. at 814. Moreover, Michigan’s inconsistent tax treatment of retired state employees and retired federal employees was not justified by “significant differences between the two classes” of employees. Id. at 817. The Court concluded that, by favoring retired state and local government employees over retired federal employees, the Michigan statute violated the principle of intergovernmental tax immunity. Id.
[220]*220The appropriate remedy, the Court announced, is a mandate of “equal treatment, a result that can be accomplished by withdrawal of benefits from the favored class as well as by extension of benefits to the excluded class.” Id. at 817-18.
“[AJppellant’s claim could be resolved either by extending the tax exemption to retired federal employees (or to all retired employees), or by eliminating the exemption for retired state and local government employees. * * * [T]he Michigan courts are in the best position to determine how to comply with the mandate of equal treatment.” Id. at 818.
This court later applied .Dacis and held that Oregon’s taxation scheme, which was similar to the Michigan taxation scheme challenged in Davis, “impermissibly discriminated against employees of the federal government in violation of the constitutional doctrine of intergovernmental tax immunity. ” Ragsdale v. Dept. of Rev., 312 Or 529, 542, 823 P2d 971 (1992).8
In response to Davis, the 1991 Oregon legislature amended ORS 237.201 (1989) by repealing the tax exemption previously granted to PERS retirement benefits. Or Laws 1991, ch 823, § 1. The 1991 legislature also repealed ORS [221]*221316.680(l)(d) (1989), which excluded PERS retirement benefits from the state taxable income base. Or Laws 1991, ch823, § 3. Following those statutory amendments, federal and PERS retirement benefits have been taxed alike under state income tax statutes.
The 1991 legislature also increased PERS retirement benefits payable to some state retirees. Or Laws 1991, ch 796. The increased PERS retirement benefits are based on an employee’s years of service and range from one percent (10 to 20 years of service) to four percent (30 or more years of service). Id. at § 6. The benefits are not calculated on actual or even potential tax liability. That is to say, there is no mathematical correlation between taxes and the benefits created in 1991. Some state retirees who will be required to pay state income taxes on their PERS retirement benefits will receive no additional benefits under the 1991 law. Conversely, some state retirees who will pay no state income taxes will receive additional benefits. The benefits received pursuant to the 1991 statute are themselves subject to state and federal income taxation. The 1991 increase in PERS retirement benefits is funded by the PERS retirement trust fund. See ORS 237.271 (the Public Employes’ Retirement Fund is a trust fund separate and distinct from the General Fund. Public employers that make contributions to the fund have no proprietary interest in the fund or in their contributions to the fund.).
Oregon Laws 1991, chapter 796, also provides that those increased PERS retirement benefits “shall not be paid in any tax year in which the retirement benefits payable under the Public Employes’ Retirement System are exempt from Oregon personal income taxation.” Id. at § 12. Oregon Laws 1991, chapter 796, section 12, further provides:
“In the event increased benefits under chapter 796, Oregon Laws 1991, are paid in a tax year in which the retirement benefits payable under the system are exempt from Oregon personal income taxation, the benefits shall not be recoverable by the system, but the Public Employes’ Retirement Board shall insure that no additional amounts are paid under the provisions of chapter 796, Oregon Laws 1991.”
Although the 1991 legislature chose to increase PERS retirement benefits payable to some state retirees, it did not extend [222]*222any reciprocal benefits to federal retirees taxed under Oregon Laws 1991, chapter 823.
Current and retired state employees affected by the 1991 legislative changes that subjected PERS retirement benefits to state income taxation sued the state for breach of their employment contracts. In Hughes v. State of Oregon, 314 Or 1, 33, 838 P2d 1018 (1992), this court held that, by subjecting PERS retirement benefits to state income taxation, the state had breached certain contracts between the state and its current and retired employees:
“[B]y repealing the tax exemption previously afforded by former ORS 316.680(l)(d) (1989), section 3 of the 1991 law results in the taxation of PERS retirement benefits, an action in breach of the tax exemption term of the PERS contract. In other words, the state has chosen, pursuant to section 3 of the 1991 law, to breach the tax exemption term of the PERS contract that the state has with its employees. This the state may not do with impunity. Anyone whose PERS benefits are contractually exempt from taxation, in whole or in part, is entitled to a remedy for the state’s breach.”
This court declined to fashion a remedy for that breach of contract, leaving it to the legislature, in the first instance, to choose among the available remedies. Id. at 33 n 36.9 Federal retirees, of course, were not parties to the Hughes litigation and, thus, they were not direct beneficiaries of its holding.
Taxpayer is a federal retiree and a resident of Oregon. During 1991, she received federal retirement benefits totaling $31,184, as compensation for services that she had rendered as an employee of the United States. The state tax liability attributable to that income was $2,865.06, which she paid in a timely manner. In 1992, taxpayer filed an amended individual income tax return requesting a refund of the $2,865.06, plus interest, arguing that Oregon impermissibly discriminated in the taxation of federal retirement benefits as compared to the taxation of PERS retirement benefits. The Department of Revenue (department) denied the refund.
[223]*223Taxpayer appealed to the Oregon Tax Court, which sustained the department’s order, explaining:
“[Taxpayer’s] argument is based on an economic analysis which assumes the state may not do with the left hand what it cannot do with the right. An appropriate response to [taxpayer’s] argument echoes the language of Davis: What the state does with regard to compensation of its employees, current or retired, is simply irrelevant to an inquiry as to the tax treatment of state and federal pensions.
“In essence, [taxpayer] argues that the state cannot change the compensation of its employees without forfeiting the right to tax federal pension income. This is the very type of interference that the doctrine of intergovernmental tax immunity was intended to prevent. Davis did not mandate that state and federal retirees must receive equal pension benefits. Rather, Davis requires that both classes must be treated equally by the state’s income tax laws. That the state may relieve its employees of the economic consequences of Davis merely demonstrates that the Supreme Court threw its net into a shallow pond. The only economic effect noted by the court in Davis was an increase in federal income taxes ‘in some circumstances.’ Davis at 816, n 4. Aside from administrative confusion and the initial costs of refunds and adjusting systems, Davis need have little economic consequence in Oregon.
“In summary, [taxpayer] has not shown or asserted any discrimination in the tax treatment of state and federal retirees. Davis does not hold or even intimate that a state is prohibited from adjusting the compensation of its employees, either currently or retired, to make up for the loss of the exemption.” Ragsdale, 13 OTR at 145-46.
Taxpayer then appealed to this court. ORS 305.445.
Taxpayer contends that the Tax Court erred in denying her claim for a refund of her personal income tax in the amount of $2,865.06, plus interest. She does not argue that any discrimination exists in the Oregon tax statutes per se, and she concedes that both federal and state retirement benefits are now taxed in like manner under the state income tax statutes. Rather, taxpayer argues that the imposition of an income tax on PERS retirement benefits by Oregon Laws 1991, chapter 823, section 3, was accompanied by a “tax rebate” to state retirees for the tax imposed, which federal retirees did not receive. Taxpayer further argues that state [224]*224retirees are entitled to a remedy for the state’s breach of contract under Hughes, 314 Or at 33, when federal retirees do not have an equivalent advantage with regard to their federal retirement benefits. Thus, taxpayer asserts, because state retirees may receive, now or later, increased PERS retirement benefits under Oregon Laws 1991, chapter 796, and contract damages under Hughes, the state discriminates against federal retirees who receive no comparable amounts. The disparate tax treatment between the recipients of PERS retirement benefits and federal retirement benefits, taxpayer asserts, violates the principle of intergovernmental tax immunity. Therefore, taxpayer maintains, she is entitled to a refund of the discriminatory tax she paid for the 1991 tax year, plus interest.
The department does not dispute that the 1991 legislature increased PERS retirement benefits to compensate state retirees, in part, for their increased income tax obligations resulting from the enactment of Oregon Laws 1991, chapter 823. However, the department does not agree with taxpayer’s argument that the legislature’s decision to make those increased payments was an exercise of the state’s taxing authority. The department argues that the state was acting consistently with its contracting authority in anticipating the need to make a contract benefit level adjustment, either as “damages” or otherwise, in contrast to its taxing authority.10
The department argues that, because Oregon taxes PERS retirement benefits and federal retirement benefits equally, and because taxpayer incorrectly equates an increase in PERS retirement benefits with a tax refund, her claim of [225]*225discrimination lacks merit. The department asserts that taxpayer has failed to recognize the distinction between a state adjustment of retirement benefit levels pursuant to contract and state action under its taxing authority.11 The department further argues that payment of increased PERS retirement benefits to state retirees is compensation for services performed by the employees and that the payment of such benefits should not be characterized mistakenly as “imposition of a tax” or “a tax rebate” because, under Hughes, state retirees are lawfully entitled to an agreed upon level of retirement compensation, regardless of the form in which it may be paid.
The Supreme Court of the United States in Davis construed 4 USC § 111 to mandate “equal treatment” of recipients of state and federal retirement benefits. Davis, 489 US at 817-18. Accordingly, and subject to a showing that any inconsistent tax treatment is directly related to, and justified by, significant differences between the classes, a state may not discriminate in taxation between state and federal retirees, based on the source of the benefits. Id. at 817. The validity of taxpayer’s argument hinges on the accuracy of her assumptions that the increased PERS retirement benefits of some state retirees under Oregon Laws 1991, chapter 796, and that the award of a remedy to PERS retirees pursuant to Hughes are, in effect, tax rebates to state retirees, which create discrimination in taxation between state and federal retirees based on the source of the benefits. Intergovernmental tax immunity, which is the legal predicate for taxpayer’s challenge, is concerned with discriminatory tax treatment. Therein lies the imperative that taxpayer be able to show that the benefits received under Oregon Laws 1991, chapter 796, are, or that any remedy under Hughes is, in effect, a tax rebate or tax benefit provided by the state only to state [226]*226retirees in a manner that discriminates against federal retirees, based on the source of the benefits.
Intergovernmental tax immunity does not require that the state treat state and federal employees the same way, it requires only that the state system of taxation be equal. The statute and the doctrine provide that the United States consents to state taxation of its employees “if the taxation does not discriminate” against them because of the source of compensation.
It is important, first, to eliminate Hughes from further discussion. As noted, the 1991 statutory amendments were not, by definition, a legislative reaction to Hughes, much less a partial legislative award of damages for the breach of contract identified by that decision. Hughes was not decided until 1992, and the application — if any — of the doctrine of intergovernmental tax immunity to final resolution of damage actions brought in the wake of Hughes must await another day.12 Taxpayer’s sole viable argument in this case concerns the 1991 legislatively directed adjustment in PERS benefits.
With respect to Oregon Laws 1991, chapter 796, that statute contains indicia that could lead one to conclude either that the “benefits” are a kind of tax rebate or that the “benefits” are compensation. The provision to end the payments if state taxation ends points toward a tax rebate. However, for the reasons that follow, we conclude that, in context, the 1991 legislation is not a tax rebate or tax benefit that would implicate the principle of intergovernmental tax immunity. Nothing in the present Oregon system discriminates in taxation against federal retirees on account of the source of compensation.
[227]*227First, reference to the text of the Davis decision itself yields no indication that the federal doctrine of intergovernmental tax immunity concerns itself with the level of compensation that a state contracts to pay or pays its state retirees. 4 USC § 111, which codifies the doctrine of intergovernmental tax immunity, provides that the United States consents to the taxation of the compensation for services performed as a federal employee (including deferred compensation in the form of a federal pension), so long as the tax does not discriminate because of the federal source of that compensation. As with the Davis decision, nothing in 4 USC § 111 purports to control or concern itself with the level of compensation that the state pays its employees and retirees.
Second, not only is there nothing express in Davis or in 4 USC § 111 that would regulate the level of compensation of state employees, it would be illogical to suggest that there is anything in the underlying principle of intergovernmental tax immunity that would invalidate a state compensation plan in aspects unrelated to the level of taxation. The doctrine of intergovernmental tax immunity recognizes that separate state compensation responsibility to its officers and employees and requires only that the state treat service to the federal government in the same way that it treats service to the state government when taxing the compensation for that service. Since 1991, Oregon has done just that. As noted, taxpayer concedes that both federal and state retirement benefits are taxed in like manner under the state income tax statutes.
Third, in Davis, the Supreme Court stated possible remedies for the intergovernmental tax immunity problem that it found in that case. The Supreme Court pointed to state cures “by extending the tax exemption to retired federal employees (or to all retired employees), or by eliminating the exemption for retired state and local government employees.” 489 US at 818. In direct response to Davis, the 1991 Oregon legislature amended ORS 237.201 to remove the tax exemption for PERS retirement benefits. That legislative act conformed Oregon law to the express dictates of Davis, by acting in a manner expressly approved by Davis.
Fourth, consistent with the points made above regarding state payment of compensation to its retirees, the [228]*228increase in benefits provided by the 1991 legislature is not part of the system of state taxation in Oregon. It does not involve the assessment or collection of revenues, which is the hallmark of a tax. See Automobile Club v. State of Oregon, 314 Or 479, 485, 840 P2d 674 (1992) (“In the most general sense, a tax is ‘any contribution imposed by government upon individuals, for the use and service of the state * * *’ ”). It involves the expenditure of trust funds, not the collection of state revenues.
The 1991 increase in compensation is not transformed into a tax rebate or tax benefit simply because it was motivated in whole or in part as a response to the Davis decision and the consequent removal of the tax exemption for PERS retirement benefits. Moreover, it is important to remember that state retirees will pay state and federal income taxes on any increased benefits they receive.
Fifth and last, we find no correlation, either direct or indirect, between state retirees’ state tax obligations and the amount of increased PERS retirement benefits, if any, to which they may be entitled under the provisions of Oregon Laws 1991, chapter 796. As noted, the amounts of increased retirement benefits are based on the PERS members’ years of service, not on their state income tax obligations. All eligible PERS retirees receive those increased benefits. Moreover, the increased benefits received pursuant to the 1991 statute are themselves subject to state and federal taxation. Indeed, taxpayer’s claim for a tax refund measured by the increased benefit paid to state retirees incorrectly assumes that every state retiree who receives an increase in benefits paid state income taxes, but it is conceivable that many state retirees paid little or no state income tax for 1991. See, e.g., ORS 316.157 (credit for retirement income).13
[229]*229In sum, taxpayer’s argument lacks both a factual and a legal predicate. The system of state taxation is not implicated by the 1991 increase in retirement benefits to some state retirees and the principle of intergovernmental tax immunity does not apply, because there is no discrimination in taxation on account of the source of compensation.
Taxpayer relies on Sheehy v. Public Employees Retirement Div., 262 Mont 129, 864 P2d 762, reh den (1993). In Sheehy, retirees challenged certain provisions of Montana law enacted in response to Davis. Before Davis, Montana, like Oregon, taxed federal retirement benefits but exempted state retirement benefits. Sheehy, 262 Mont at 132, 864 P2d at 764.
The Montana Supreme Court described the 1991 Montana legislature’s response to Davis as follows:
“The Montana legislature subsequently passed Chapter 823, 1991 Montana Laws, which, according to its title, restructures the income tax on pension benefits by equalizing the taxation of all pension benefits. In lieu of extending the total exemption from taxation previously available to state retirement income to federal retirement income, the legislature opted in Chapter 823 to bring all retirement income — including both state and federal pensions — within the Montana income tax. * * *. In addition, section 5 of Chapter 823 grants to state retirees who are Montana residents, and who now were to be taxed in response to Davis, an annual retirement adjustment payment.” Sheehy, 262 Mont at 132-33, 864 P2d at 764.
The Montana court concluded that the provisions of Montana Laws 1991, chapter 823, section 5, constituted discriminatory taxation in violation of the intergovernmental tax immunity provisions of 4 USC § 111, explaining:
“It is clear that the adjustment is not an actual and legitimate pension or retirement benefit. If it were a pension benefit, the State would have provided it to all of its retirees in recognition of their years of public service rather than just those living in Montana. There was no need to do so because the sole purpose of the adjustment was to partially recompense state retirees living in Montana for the tax they now must pay under the equalizing provisions of Chapter 823.
[230]*230“Further evidence that the adjustment is not an actual increased retirement benefit for retired state employees is the fact that the funding of the section 5 adjustment bears no resemblance to the funding of actual state retirement benefit adjustments previously enacted by the legislature. [Such previous enactments were] funded by investment income produced by the retirement fund made up of employee and employer contributions. Here, the funding for the so-called retirement adjustment payment is statutorily appropriated from the general fund * * *.
“We conclude that the adjustment is a partial tax rebate denominated otherwise in an attempt to evade the requirements of federal law.” lb. at 138-39, 864P2dat768 (citation omitted; emphasis in original).
Taxpayer argues that, Oregon Laws 1991, chapter 796, like the Montana enactment examined in Sheehy, is a partial tax rebate for state retirees and, therefore, that it constitutes discriminatory taxation of federal retirees who do not receive the same benefits. We disagree.
The Sheehy court’s conclusion that the Montana adjustment is a partial tax rebate that violated federal law relied heavily on two features of the Montana enactment: (1) that only retirees who are Montana residents will receive the benefit, and (2) that the retirement benefits at issue are funded solely by the Montana general fund.
In contrast, under Oregon Laws 1991, chapter 796, every state retiree who qualifies for benefits (based on years of service) will receive the benefits, regardless of the state retiree’s residency. Moreover, the challenged provisions of Oregon Laws 1991, chapter 796, do not appropriate money from the Oregon general fund. Rather, the increased PERS retirement benefits are funded by contributions from all PERS employers to the PERS retirement trust fund. Or Laws 1991, ch 796, § 3.14
Intergovernmental tax immunity is based on the need to protect each sovereign’s governmental operations [231]*231from undue interference by the other. Davis, 489 US at 814. We agree with the Tax Court that “Davis does not hold, or even intimate that a state is prohibited from adjusting the compensation of its employees, either currently or retired, to make up for the loss of the [income tax] exemption.” Ragsdale, 13 OTR at 146.15
Justice Gillette, dissenting, concludes that the state retirees’ increased PERS retirement benefits are, in fact, a partial refund of state income taxes paid by state retirees on their PERS retirement income and would hold:
“So long as there is a direct tie between state income taxation of PERS retirement benefits and the availability of increased PERS retirement benefits, it is not even necessary to inquire whether there are other, additional grounds on which to declare the present taxation scheme to be impermissibly discriminatory.” 321 Or at 234 (Gillette, J., dissenting).
We are not persuaded by that analysis.
A tax rebate or tax benefit program only for state employees clearly would be impermissible. The Oregon law, however, is not a tax rebate program or a tax benefit. Everyone’s income is taxed equally. The state is entitled to raise the level of taxable compensation of its employees, for whatever reason, including to compensate them for a change in the tax laws that results in a decreased level of net after-tax income.
For example, if the state government changed the state tax laws to limit the deduction for mortgage payments and chose to raise the level of state employees’ compensation because of the change, that should not violate the federal law. Everyone is taxed in the same way; the state can pay its employees what it wants to pay them. Nor should it be deemed to violate the federal law if the raise is good only for as long as the tax law change is good, which is Justice Gillette’s point of departure. That tie-in defines the duration of the change in taxable compensation, but it has no impact on the comparative equity of the state system of taxation.
[232]*232Nowhere in the federal doctrine of intergovernmental tax immunity is there the idea that a state’s choice to expend more of its money on the compensation of state governmental employees violates the doctrine. That choice by the state may or may not increase the overall tax burden on everyone (state and federal public employees, private wage earners, businesses) depending on budget and taxation choices made by the legislature. Those are policy choices, subject to a watchful electorate that includes a vast majority of people who are not state employees, but they do not raise intergovernmental tax immunity concerns.
The state should be free to compensate its employees with its eyes open to the tax burdens that it places on them. We do not believe that the Supreme Court of the United States would assert that the principle of intergovernmental tax immunity deprives the state of its sovereignty to fix the level of its employees’ compensation and to ensure that their net after-tax income is at a level commensurate with the agreement of the employees and the state. Federal employees lose the right to complain about inequality in the state tax system when the system treats them equally. Oregon now does that. Justice Gillette’s analysis focuses on one fact, the durational tie-in to the tax laws of the raise in compensation, to the unwarranted exclusion of literally everything else. In context, we do not believe that that tie-in supports taxpayer’s claim here.
Justice Fadeley, who concurred in part with this court’s holding in Hughes that PERS retirement benefits accrued or accruing for work performed on or before September 28, 1991, may not be taxed, would have gone further in Hughes to hold that any action to tax PERS retirement benefits under Oregon Laws 1991, chapter 823, section 3, was unconstitutional. Hughes, 314 Or at 37-38 (Fadeley, J., concurring in part and dissenting in part). Implicit in his analysis is a conclusion that, under Davis, the state’s only recourse is to exempt state and retirees’ retirement benefits from state income taxation. In this case, Justice Fadeley pursues that same analysis to conclude that federal retirement income must be exempt from state income taxation. 321 Or at 235-36 (Fadeley, J., dissenting). His conclusion, however, is based on a faulty premise, i.e., that the state could not tax PERS [233]*233retirement benefits. As this court held in Hughes, the state may tax PERS retirement benefits but, in doing so, the state became liable for damages for breach of contract. Because the state may tax PERS retirement benefits and does so, the state does not discriminate against federal retirees when it taxes federal retirement benefits equally.
We hold that the benefits paid to state retirees, pursuant to Oregon Laws 1991, chapter 796, do not give rise to a violation of 4 USC § 111 and the constitutional principle of intergovernmental tax immunity.
The judgment of the Tax Court is affirmed.
‘The United States consents to the taxation of pay or compensation for personal service as an officer or employee of the United States * * * by a duly constituted taxing authority having jurisdiction, if the taxation does not discriminate against the officer or employee because of the source of the pay or compensation.’ 4U.S.C. § 111.”