NBC claimed Friday that any attempt by the Writers Guild of America to enforce strike rules barring Jay Leno from writing his monologue for the Tonight show would violate federal labor laws. It did not specify which labor laws would be violated. Meanwhile Screen Actors Guild President Alan Rosenberg issued a statement that appeared to encourage actors to appear on The Late Show With David Letterman and Late Late Show With Craig Ferguson -- which have signed separate agreements with the WGA -- and discourage actors from appearing on NBC- and ABC-produced talk shows. "As I have said since this strike began on November 5th," Rosenberg said, "we must stand united with our brothers and sisters at the WGA."