Basically the problem is that a law passed to reconcile U.S. copyright law with the international treaties that we agreed to in 1988 and after had the effect of removing some works from the public domain. This had virtually never happened before; until the Uruguay Round Agreements Act (URAA) of 1994, things that were in the public domain stayed there, and users could safely depend on their availability for use and reuse. For a subset of materials, however, the URAA changed the rules pretty dramatically and, according to the petitioners, in a way that conflicts with the basic protection of free speech found in the US Constitution.