In Perez v. United States, the Supreme Court examined whether a federal law prohibiting interstate travel with intent to commit murder in violation of state laws was constitutional. The defendant, Perez, had been convicted under this law for traveling from New York to Florida with the intention of carrying out a contract killing. He appealed his conviction on grounds that Congress lacked authority to enact such legislation and that it violated his Fifth Amendment rights by being overly vague. However, the Supreme Court upheld both the constitutionality of the statute and Perez's conviction in 1970. It ruled that Congress has broad power under the Commerce Clause to regulate interstate activities which negatively impact commerce or use channels of commerce for illicit purposes; thus validating its authority over criminal acts crossing state lines even if they are primarily regulated by states' police powers.

In the dissenting opinion for Perez v. United States, Justice Hugo Black argued that the federal government did not have constitutional authority to regulate loan sharking as it was a local criminal activity and not interstate commerce. He contended that Congress had overstepped its bounds by using the Commerce Clause of the Constitution to justify regulation of activities traditionally handled at state level. Furthermore, he expressed concern about potential abuse of power if such broad interpretation were allowed to stand unchallenged; he feared this could lead to federal intrusion into areas reserved for states under Tenth Amendment. In his view, allowing Congress unlimited regulatory power would undermine principles of federalism and threaten individual liberties protected by Bill of Rights.