Jason Richards and Fannie Hill (Ps) are privately employed in Jefferson County, Alabama. In 1991 they filed a complaint in the Federal District Court challenging the validity of the occupation tax imposed by Jefferson County Ordinance 1120, which had been adopted in 1987. That action was dismissed as barred by the Tax Injunction Act, 28 U. S. C. Section(s) 1341. 1 They then commenced this action in the Circuit Court of Jefferson County. Ps represent a class of all nonfederal employees subject to the county's tax. It is alleged that the tax violates the Due Process and Equal Protection Clauses of the Fourteenth Amendment and similar provisions of the Alabama Constitution. Because $10 million of the annual proceeds from the county tax have been pledged to the Birmingham-Jefferson Civic Center for a period of 20 years, the court permitted the Center to intervene and support Jefferson County's defense of its tax. D moved for summary judgment on the ground that Ps' claims were barred by a prior adjudication of the tax in an earlier action brought by the acting director of finance for the city of Birmingham and the city itself. That earlier action had been consolidated for trial with a separate suit brought by three county taxpayers, and the Supreme Court of Alabama upheld the tax in the resulting appeal. The trial court granted the county's motion for summary judgment as to the state constitutional claims, but refused to do so as to the federal claims because they had not been decided by either the trial court or the Alabama Supreme Court. On appeal, D argued that the federal claims, as well as the state claims, were barred by the prior adjudication in Bedingfield. The Alabama Supreme Court agreed. A prior judgment on the merits rendered by a court of competent jurisdiction precludes the relitigation of a claim if there is a 'substantial identity of the parties' and if the 'same cause of action' is presented in both suits. The prior judgment is generally res judicata not only as to all matters litigated and decided by it but as to all relevant issues which could have been but were not raised and litigated in the suit. The Alabama Supreme Court concluded that even though the opinion in Bedingfield did not mention any federal issue, the judgment, in that case, met these requirements. The court gave three reasons for this conclusion: (1) the complaints in the earlier case had alleged that the county tax violated the Equal Protection Clause of the Fourteenth Amendment and an equal protection issue had been argued in the appellate briefs; (2) the taxpayers adequately represented Ps because their respective interests were 'essentially identical; and (3) in pledging tax revenues and issuing bonds in 1989, D could have relied on Bedingfield as authoritatively establishing that the county occupational tax was not unconstitutional for the reasons asserted by the previous plaintiffs. The Supreme Court granted certiorari.