Channels of commerce represent a broad congressional power which directly regulates the movement of goods and people across state lines. Importantly, the Court has never required a nexus (causal link) between a state border crossing and the engagement of an activity prohibited by Congress. In "United States v. Sullivan" (1948), the Court held that Section 301k of the Federal Food, Drug, and Cosmetic Act, which prohibited the misbranding of pharmaceutical drugs which had been transported in interstate commerce, did not exceed the congressional commerce power because Congress has the power to “keep the channels of such commerce free from the transportation of illicit or harmful articles.” Topics in this category include mailing or shipping in interstate commerce, prohibiting crimes where the individual crossed a state line to commit the act, and explosives.