As a federal statute, the NLRA preempts, or displaces, many aspects of state law. Three main rules govern NLRA preemption.

I. Mandatory Preemption

Mandatory preemption is also known as Garmon preemption, after the case that established the rule. San Diego Bldg. & Trades Council v. Garmon, 359 U.S. 236 (1959).

Suppose a union suspended Terry from membership because of unpaid dues. Following the suspension, his employer fired Terry because the applicable CBA required employees to be union...