In upholding a state statute regulating navigation standards for ships, the Supreme Court formulated the doctrine of selective exclusiveness, allowing states to regulate aspects of interstate commerce in the absence of federal laws.

A Pennsylvania law required each ship entering or leaving Philadelphia to hire a local pilot for navigation purposes. When Aaron Cooley was fined for disobeying the law, he argued that it was an unconstitutional regulation of interstate commerce. By a 6-2 vote, the Supreme Court rejected his argument. Speaking for the majority, Justice Benjamin R. CurtisCurtis, Benjamin R.;Cooley v. Board of Wardens of the Port of Philadelphia[Cooley v. Board of Wardens of the Port of Philadelphia] made a distinction between activities needing a single national rule and other activities, such as pilotage laws, that were essentially local in nature. In the latter category, states retained a concurrent authority until Congress exerted its paramount power. The Cooley rule was essentially a compromise that allowed states to exercise limited control over interstate commerce, and it operated as a practical formula for nearly a century.Interstate commerce;Cooley v. Board of Wardens of the Port of Philadelphia[Cooley v. Board of Wardens of the Port of Philadelphia]

Commerce, regulation of

Passenger Cases

Pennsylvania v. Wheeling and Belmont Bridge Co.

Police powers