The U.S. Supreme Court case Katzenbach v. Morgan (1966) was a landmark decision that upheld the power of Congress to enact broad and sweeping legislation under Section 5 of the Fourteenth Amendment, also known as the Enforcement Clause. The case involved New York State's English-language literacy requirement for voting, which was challenged by Puerto Rican residents who were educated in Spanish-speaking schools. They argued that this requirement violated their rights protected by the Equal Protection Clause of the Fourteenth Amendment. In a 7-2 decision led by Justice William J Brennan Jr., it ruled in favor of Morgan et al., stating that Congress had authority under Section 5 to enforce civil rights protections beyond what courts had previously recognized or enforced themselves - including eliminating state laws like literacy tests if they discriminated against minority voters.

In the dissenting opinion for Katzenbach v. Morgan, Justice Harlan argued that Section 4(e) of the Voting Rights Act was unconstitutional because it exceeded Congress's enforcement powers under the Fourteenth Amendment. He maintained that this section, which prohibited states from denying voting rights to certain Puerto Rican-born citizens based on English literacy tests, intruded upon state sovereignty and violated principles of federalism by dictating specific policies to states. Furthermore, he contended that such a provision should be subject to judicial review rather than being left solely in congressional hands. In his view, while Congress had broad power to enforce constitutional amendments through appropriate legislation, it did not have unlimited authority to determine what constituted a violation of those amendments.