I don't know of a statute that makes it illegal to attempt to restrict access to works legally in the public domain, so no, I don't think that implication follows. Once a classified work is public, however, the government cannot assert copyright. They must use clauses in laws such as the Espionage Act to attack the release, and the Supreme Court has not looked kindly upon those attemptsº.

ºhttp://en.wikipedia.org/wiki/New_York_Times_Co._v._United_St...