392 U.S. 83 (1968), argued 12 Mar. 1968, decided 10 June 1968 by vote of 8 to 1; Warren for the Court, Douglas, Stewart, and Fortas concurring separately, Harlan in dissent. A group of taxpayers sued to enjoin the allegedly unconstitutional expenditure of federal funds for the teaching of secular subjects in parochial schools. A federal court decided that they lacked standing to sue as taxpayers under Frothingham v. Mellon (1923), but the Supreme Court reversed and held that, under certain limited circumstances, taxpayers could sue in federal courts to challenge federal expenditures.
Chief Justice Earl Warren's opinion rejected the contention that Frothingham articulated a constitutional requirement that absolutely barred taxpayer suits. Rather, he said, Frothingham was more deeply rooted in policy considerations that permitted greater discretion to federal judges to entertain such suits. Taxpayer suits would be permitted if the petitioner was a proper and appropriate party to invoke federal judicial power. Standing to sue would be measured by a two-part test: first, a taxpayer could challenge the constitutionality only of the exercise of congressional power under the Taxing and Spending Clause of Article I, section 8. It would not be enough merely to challenge “incidental” expenditures under Congress's enumerated powers; second, the taxpayer must show that the challenged enactment is prohibited by a specific constitutional limitation on Congress's taxing and spending power and not merely by a general limitation on its powers, such as the Tenth Amendment.
Flast satisfied both requirements. She challenged an expenditure under the Taxing and Spending Clause alleging it violated the establishment and free exercise clauses of the First Amendment. Frothingham would have met the firxt nexus, but not the second. She had challenged the Maternity Act of 1921, which was enacted under the Taxing and Spending Clause; but she claimed only that it violated Congress's general legislative powers, the Due Process Clause of the Fifth Amendment, and the Tenth Amendment. Thus in Flast the Court was able to distinguish Frothingham without overruling it.
Justice William O. Douglas, urging the widest latitude for “private attorneys general” to sue (and thus broad taxpayer access to the courts), argued that Frothingham was incompatible with the spirit if not the holding in Flast, and should be overruled. In dissent, Justice John M. Harlan conceded that Frothingham was too rigid and should be modified but contended that Flast went too far and would open the courts to abuse that strained the judicial function.
Flast was central to the Warren Court's liberal activist philosophy of increasing public access to federal courts and making them more receptive to public law litigation. But it remained unclear how far the decision went in removing traditional barriers to such litigation. Warren formally declined to speculate on whether “the Constitution contains other specific limitations” on the taxing and spending power (p. 105). But Flast was widely seen as an invitation to litigants to seek redress of their constitutional grievances in the federal courts without having to demonstrate the traditional personal injury or harm. A flood of taxpayer lawsuits, many challenging the legality of the war in Vietnam, followed.