Current US Copyright laws are not explicit that edicts of government (be they federal, state, or local) cannot be copyrighted. The right to know the law is vital to obeying it. A SCOTUS case in 1834 affirmed this, but various states have gradually infringed on it. For example, it's illegal in various states to copy their laws, e.g., publish on a website, without paying a large fee. The Amendment text reads as follows:
"Edicts of government, such as judicial opinions, administrative rulings, legislative enactments, public ordinances, and similar official legal documents are not copyrightable for reasons of public policy. This applies to such works whether they are Federal, State, or local as well as to those of foreign governments."
Congressional testimony: Public.Resource.org/edicts