Early on, in the so-called Civil Rights Cases decided in 1883, the Supreme Court concluded that the Congressional enforcement power in Section 5 of the Fourteenth Amendment did not authorize Congress use the Privileges or Immunities Clause of that amendment to ban racial discrimination in public accommodations operated by private persons, such as inns and theaters. The Court stated that since the Fourteenth Amendment only restricted state action, Congress lacked power under this amendment to forbid discrimination that was not sponsored by the state. This ruling has not been overturned, however, in modern times, similar civil rights legislation has been upheld under Congress's power to regulate interstate commerce under Article One, Section 8 of the Constitution. See Civil Rights Act of 1964.
In the Katzenbach v. Morgan case, decided in 1966, the Supreme Court concluded that Congress can forbid practices that are not themselves unconstitutional, if the law is aimed at preventing or remedying constitutional violations. On that basis, the Court upheld a provision of the Voting Rights Act that prevented states from using English language literacy tests as qualifications for voting. The Court decided that the law was a valid exercise of Congress's enforcement power under the Equal Protections Clause of Fourteenth Amendment, because it was aimed at remedying state-sponsored discrimination, despite an earlier court finding that a literacy test was not in and of itself a violation of the 14th Amendment.
In 1970, however, in Oregon v. Mitchell, the Court held that Congress had exceeded its power by attempting to require the states to reduce the voting age to 18. This led to adoption of the Twenty-Sixth Amendment to the Constitution in 1971, which provided that the states could not set a minimum voting age higher than 18.
In the 1997 case of City of Boerne v. Flores, the Court again took a narrow view of the Congressional power of enforcement, striking down a provision of the Religious Freedom Restoration Act (RFRA) that sought to forbid the states from placing burdens on religious practice in the absence of a compelling state interest in doing so. In enacting RFRA, Congress had sought to overturn the 1988 Supreme Court decision in Employment Division v. Smith, which had held that the Constitution does not require states to recognize religious exemptions to laws of general applicability. In the Boerne case, the Supreme Court decided that RFRA overstepped Congress's authority, because the statute was not sufficiently connected to the goal of remedying a constitutional violation, but instead created new rights that are not guaranteed by the Constitution. Some observers have suggested that the Supreme Court saw RFRA as a threat to the Court's institutional power and an incursion on its role as final arbiter of the meaning of the Constitution, because that statute was aimed specifically at overturning the Employment Division v. Smith decision. However, the effect of Boerne lasted beyond Boerne itself. The standard announced in that case--that all legislation enacted under section 5 of the Fourteenth Amendment must be "congruent and proportional" to the unconstitutional harm it seeks to remedy--has been followed by every post-Boerne decision on legislation that sought to abrogate the states' sovereign immunity. Boerne and its progeny have been much criticized by scholars, including, most notably, John T. Noonan, Jr., a senior judge of the United States Court of Appeals for the Ninth Circuit and a professor at Boalt Hall.
United States v. Morrison, decided in 2000, is one controversial successor case. In that case, the Supreme Court, applying the congruent-and-proportional Boerne test, overturned provisions of the Violence Against Women Act (VAWA), which criminalized gender-based violence. The Court held that Congress did not have power to forbid discrimination against women in the absence of a connection to state action or interstate commerce. But see Tennessee v. Lane and Nevada Department of Human Resources v. Hibbs.