Federal law preempts state law under three circumstances:
- "express preemption," where Congress explicitly preempts state law
- "field preemption," where Congress implicitly preempts state law by "occupying the entire field, leaving no room for the operation of state law"
- "conflict preemption," where courts infer preemption because "compliance with both state and federal law would be impossible, or state law stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress."
Courts presume that federal law does not preempt "state law in areas traditionally regulated by the States."
- Aerocon Eng'g, Inc., v. Silicon Valley Bank (In re World Aux. Power Co.), 303 F.3d 1120 (9th Cir. 2002) (quoting Keams v. Tempe Technical Institute, Inc., 39 F.3d 222, 225 (9th Cir. 1994)).