Under the Federal Constitution's Supremacy Clause, Congress has the power to preempt state and local laws, rendering them "null, void, invalid and inoperative." Congress often exercises this power by adopting statutory provisions that expressly preempt certain forms of state or local regulation. The traditional answer to whether federal preemption treats state law and local (city or county) law the same has been an unequivocal yes.
"Preemption Conflation: Dividing the Local from the State in Congressional Decision Making,"
Yale Law & Policy Review: Vol. 30
, Article 3.
Available at: http://digitalcommons.law.yale.edu/ylpr/vol30/iss2/3