Wickard v. Filburn, 317 U.S. 111 (1942), was a U.S. Supreme Court decision that dramatically increased the power of the federal government to regulate economic activity. A farmer, Roscoe Filburn, was growing wheat to feed his chickens. The U.S. government had imposed limits on wheat production based on acreage owned by a farmer, in order to drive up wheat prices during the Great Depression, and Filburn was growing more than the limits permitted. Filburn was ordered to destroy his crops and pay a fine, even though he was producing the excess wheat for his own use and had no intention of selling it.
Prior to this, Congress could only regulate what crossed state lines. Now they could regulate anything.
http://en.wikipedia.org/wiki/Wickard_v._Filburn
