Federal preemption is the doctrine that when federal and state laws conflict, federal law takes precedence and displaces state law. The Supremacy Clause of Article VI establishes this hierarchy: "This Constitution, and the laws of the United States which shall be made in pursuance thereof... shall be the supreme Law of the Land." Preemption applies regardless of when laws were enacted—an older state law is preempted if it conflicts with newer federal law, and vice versa.
Courts recognize three types of federal preemption. Express preemption occurs when Congress explicitly states a federal law preempts state law. Implied preemption occurs when federal law is so comprehensive that Congress clearly intended to occupy the entire field, leaving no room for state regulation. Conflict preemption occurs when state law directly conflicts with federal law—for example, when state law permits an action the federal government forbids. The challenge lies in determining when conflict or comprehensive federal regulation actually exists, since courts prefer interpretations that avoid preempting state laws when possible.
Real-world examples illustrate the complexity. Marijuana remains illegal under federal law while 24 states legalized recreational use, creating a preemption ambiguity: federal law technically preempts, but the Biden administration deprioritized enforcement. Immigration enforcement creates similar tensions—Texas passed a law allowing state judges to order deportations, but the Fifth Circuit struck it down, holding that immigration belongs exclusively to federal authority. Federal preemption ensures national standards on issues affecting interstate commerce, but also limits state flexibility to address local concerns.
Preemption determines which level of government has the final say when federal and state laws clash. It's why states cannot override federal constitutional rights, why federal environmental standards supersede state environmental rules, and why state marijuana legalization doesn't override federal prohibition.
People often think states can ignore federal law if they disagree. In practice, when Congress validly exercises its enumerated powers, the Supremacy Clause makes federal law binding despite state objections.
Preemption determines which level of government has the final say when federal and state laws clash. It's why states cannot override federal constitutional rights, why federal environmental standards supersede state environmental rules, and why state marijuana legalization doesn't override federal prohibition.
People often think states can ignore federal law if they disagree. In practice, when Congress validly exercises its enumerated powers, the Supremacy Clause makes federal law binding despite state objections.