The Supreme Court case that established the precedent that the federal government can regulate economic activities that have a substantial effect on interstate commerce is Wickard v. Filburn (1942).

In this case, the Supreme Court upheld a federal law that set limits on the amount of wheat that farmers could grow, even if the wheat was intended for personal use on the farm. The defendant, Roscoe Filburn, had grown more wheat than he was allowed to under the law, but argued that it was for his own consumption and had no effect on interstate commerce.

The Court rejected Filburn's argument, reasoning that if all farmers grew extra wheat for personal use, it could have a substantial effect on the national wheat market and therefore on interstate commerce. This case established the principle that the federal government has the power to regulate economic activities that have a substantial effect on interstate commerce, even if the activities are purely local and not intended for sale.