Originally Posted by
Lobbyist
"This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding..."
-Article VI, Section 1, Clause 2, US Constitution
"A state statute is void to the extent that it actually conflicts with a valid Federal statute."
- USSC, Edgar v. Mite Corporation, 457 U.S. 624
First bit is pretty clear. Second bit, the laws of the united states can't be made where the united states don't have authority.