On petition for writ of certiorari to the Supreme Court of Kansas.
White, J., delivered the opinion for a unanimous Court. Stevens, J., filed a concurring opinion, in which Thomas, J., joined.
JUSTICE WHITE delivered the opinion of the Court.
The State of Kansas taxes the benefits received from the United States by military retirees but does not tax the benefits received by retired state and local government employees. Kan. Stat. Ann. § 79-3201 et seq. (1989).*fn1 The issue before us is whether the tax imposed on the military retirees is inconsistent with 4 U.S.C. § 111, which provides:
"The United States consents to the taxation of pay or compensation for personal service as an officer or employee of the United States, a territory or possession or political subdivision thereof, the government of the District of Columbia, or an agency or instrumentality of one or more of the foregoing, 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."
Shortly after our decision in Davis v. Michigan Dept. of Treasury, 489 U.S. 803 (1989), which invalidated under § 111 the Michigan income tax imposed on federal civil service retirees, two class actions were filed in Kansas District Court challenging the state income tax imposed on military retirement benefits. Together the classes comprised some 14,000 military retirees, who received federal armed forces retirement benefits and were subject to the Kansas income tax for one or more of the tax years from 1984 through 1989. The classes also included spouses of the retirees, where applicable. Plaintiff taxpayers sought a declaratory judgment that the Kansas income tax discriminates against them in favor of state and local government retirees, in violation of § 111 and the constitutional principles of intergovernmental tax immunity applied in Davis. They also requested a permanent injunction to prohibit assessment of the tax against military retirees, as well as refunds of any taxes paid by class members for the tax years 1984 through 1989.*fn2 The District Court granted summary judgment for the defendants, and the Supreme Court of Kansas affirmed. We granted certiorari because the holding below is arguably inconsistent with our decision in Davis and conflicts with decisions of other state courts of last resort. 502 U.S. (1991).*fn3
Our approach to deciding this case is controlled by Davis, which invalidated a Michigan law that imposed taxes on federal civil service retirees' benefits but not on benefits received by state and local government retirees. In reaching that decision, we traced the history of 4 U.S.C. § 111 and concluded that "the retention of immunity in § 111 is coextensive with the prohibition against discriminatory taxes embodied in the modern constitutional doctrine of intergovernmental tax immunity." 489 U.S., at 813. Under that doctrine, we evaluate a state tax that is alleged to discriminate against federal employees in favor of state employees by inquiring "whether the inconsistent tax treatment is directly related to, and justified by, significant differences between the two classes."' Id., at 816 (quoting Phillips Chemical Co. v. Dumas Independent School Dist., 361 U.S. 376, 383 (1960)).
Well aware of Davis, the State Supreme Court undertook such an inquiry and concluded that significant differences existed between military retirees, who are taxed by Kansas, and state and local government retirees, who are not. The court proceeded to consider the State's six proffered distinctions between military retirees and state and local government pensioners:
"(1) Federal military retirees remain members of the armed forces of the United States after they retire from active duty; they are retired from active duty only; (2) federal military retirees are subject to the Uniform Code of Military Justice (UCMJ) and may be court martialed for offenses committed after retirement; (3) they are subject to restrictions on civilian employment after retirement; (4) federal military retirees are subject to involuntary recall; (5) federal military retirement benefits are not deferred compensation but current pay for continued readiness to return to duty; and (6) the federal military retirement system is noncontributory and funded by annual appropriations from Congress; thus, all benefits received by military retirees have never been subject to tax." 249 Kan. 186, 196, 815 P. 2d 46, 53 (1991).
The court deemed the first four differences significant, not because in themselves they justified disparate tax treatment, but because they supported the fifth distinction -- that military retirement benefits constitute reduced pay for reduced current services, rather than deferred compensation for past services. Id., at 197, 815 P. 2d, at 53. By contrast, "state and local government retirement benefits are deferred compensation," the court found, and not current pay." Ibid. The court concluded that this principal distinction between military retirees and state and local government retirees justified their differential treatment under the State's tax laws. Accordingly, it held that a military retiree's benefits were as legally subject to state taxation as the income of active military personnel, whose pay was liable for state taxation pursuant to the United States' consent, as expressed in 4 U.S.C. § 111.
Military retirees unquestionably remain in the service and are subject to restrictions and recall; in these respects they are different from other retirees, including the state and local government retirees whom Kansas does not tax. But these differences, standing alone, do not justify the differential tax treatment at issue in this case. Nor do these differences persuasively indicate that, for purposes of 4 U.S.C. § 111, Kansas may treat military retirement pay as reduced pay for reduced services. As a general matter, a military retiree is entitled to a stated percentage of the pay level achieved at retirement, multiplied by the years of creditable service. Brief for United States as Amicus Curiae 11, n. 16. In this respect, "retired [military] pay bears some of the features of deferred compensation. The amount of retired pay a service member receives is calculated not on the basis of the continuing duties he actually performs, but on the basis of years served on active duty and the rank obtained prior to retirement." McCarty v. McCarty, 453 U.S. 210, 223, n. 16 (1981). By taking into account years of service, the formula used to calculate retirement benefits leaves open the possibility of creating disparities among members of the same preretirement rank. Such disparities cannot be explained on the basis of "current pay for current "services," since presumably retirees subject to these benefit differentials would be performing the same services." Furthermore, military benefits are determined in a manner very similar to that of the Kansas Public Employee Retirement System. Brief for United States as Amicus Curiae 11, n. 16. In terms of calculating retirement benefits, therefore, we see no significant differences between military retirees and state and local government retirees that justify disparate tax treatment by the State.
In holding to the contrary, however, the Kansas Supreme Court found support in some of our precedents. In United States v. Tyler, 105 U.S. 244 (1882), for example, the Court decided that officers retired from active military service were entitled to the same percentage increase in pay that a statute had provided for active officers. The Court reached this result in part by characterizing military retirement pay as "compensation [that] is continued at a reduced rate, and the connection is continued, with a retirement from active service only." Id., at 245.*fn4
The State Supreme Court also found support in McCarty, supra. In that case the California courts considered the applicability of state community property laws to the military retirement benefits for which an officer who had 18 years of service would be eligible 2 years hence. The California courts had held these benefits subject to division upon dissolution of the marriage. In this Court the officer challenged the holding on two grounds: first, that his prospective retirement benefits would be current pay, not subject to division as deferred compensation for services performed during the marriage; and second, that applying the community property law to retirement benefits conflicted with the federal military scheme regardless of whether retired pay is current income or deferred compensation. See id., at 221. Citing and quoting Tyler, supra, our opinion noted that military retirees differed in some respects from other retired federal personnel and that these differences had led various courts, "including this one," to opine that military retirement pay is reduced compensation for reduced current services. 453 U.S., at 222. We found no need, however, to decide "whether federal law prohibits a State from characterizing retired pay as deferred compensation," because we sustained petitioner's alternative ground for overturning the judgment below. Id., at 223.
The Kansas Supreme Court reasoned that McCarty 's recognition of the Tyler holding, as well as the decisions of several Courts of Appeals, indicated that Tyler controlled the description of military retirement pay. It thus concluded that taxing military retirement pay as current income could not validly be characterized as discriminating in favor of state and local government employees, whose benefits were exempt as being deferred compensation for past ...