gag law

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A law that limits speech, such as that of public officials. Gag laws have in some cases been ruled unconstitutional for infringing upon freedoms granted by the First Amendment.

from the GNU version of the Collaborative International Dictionary of English.

• (Parliamentary Law), Colloq. or Cant A law or ruling prohibiting proper or free debate, as in closure.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a rule for limiting or ending debate in a deliberative body
• noun any law that limits freedom of the press