Seriously. Well, I don't know how serious it is. It may just be a PR stunt. The named defendants are the WTO, USTR Ron Kirk, Secretary of Agriculture Tom Vilsack, and the United States of America. The complaint is here. An excerpt:
plaintiffs seek a declaration that the World Trade Organization has no authority to override U.S. law and that its decision concerning the Country of Origin Labeling Act is void in the United States and throughout the world.
