In the case of Hoke and Economides v. United States in 1912, the U.S. Supreme Court upheld the constitutionality of the Mann Act, also known as White-Slave Traffic Act. The defendants were charged with transporting women across state lines for "immoral purposes". They argued that Congress did not have authority under the Commerce Clause to regulate private moral matters such as sexual behavior or prostitution. However, their argument was rejected by a unanimous court which held that transportation of individuals across state lines constituted interstate commerce and thus fell within congressional power to regulate it even if its purpose was immoral activity like prostitution. This ruling expanded federal jurisdiction over criminal law enforcement traditionally reserved for states.

In the dissenting opinion for Hoke and Economides v. United States, Justice Harlan argued that Congress had overstepped its constitutional authority by passing the Mann Act under the guise of regulating interstate commerce. He contended that while Congress has broad powers to regulate trade between states, it does not have unlimited power to legislate morality or criminal behavior within individual states. In his view, matters such as prostitution were clearly within state jurisdiction and should be left up to each state's discretion rather than being federally regulated through laws like the Mann Act. He also expressed concern about potential abuses of federal power if this interpretation was allowed to stand unchallenged.