Preemption
Preemption is the doctrine under which valid federal law displaces conflicting state law. It may arise because Congress expressly states that federal law displaces state rules, because federal law occupies a field, or because state law conflicts with federal law.
Preemption is the doctrine under which valid federal law displaces conflicting state law. It may arise because Congress expressly states that federal law displaces state rules, because federal law occupies a field, or because state law conflicts with federal law.
Example: In Hines v. Davidowitz (1941), the Supreme Court held that federal alien-registration law preempted a conflicting Pennsylvania statute.
Common misconception: Any federal rule automatically overrides any state action in every circumstance. Preemption depends on valid federal authority, statutory intent, and the nature of the conflict or regulatory field.
Sources: https://constitution.congress.gov/browse/essay/artVI-C2-1/ALDE_00013388/; https://supreme.justia.com/cases/federal/us/331/230/