Preemption is a doctrine in constitutional law that applies when two authorities conflict with one another. It refers to the idea that a higher authority of law will displace the law of a lower authority of law when the two authorities come into conflict.

Federal law is the highest authority; therefore, federal law supersedes or supplants any state or local regulation or statute that conflicts it. This doctrine comes from the Supremacy Clause of the United States Constitution (U.S. Const. art. VI., § 2). 

For instance, FDA regulations will preempt any state court judgments or state laws that involve drug prescriptions. However, federal law does not preempt the state laws on labeling prescription drugs. Congress only permits federal regulatory agencies to set a minimum standard, thus not preventing each state from imposing a further standard on labeling. The Supreme Court of the United States looks into the intent of the lawmakers when there is a conflict between state and federal law. 

The preemption doctrine does not just apply at the state-federal level. States could also use the preemption doctrine to regulate and limit its municipalities from self-regulation for various issues. For determining when state law preemption should be applied when in conflict with local municipalities, the courts will look into three categories: outright conflict, express preemption, and implied preemption.

  • Outright conflict is when a state law and an ordinance are in a direct conflict with one another.
  • Express preemption is when a local power and a state law are in a direct conflict with one another.
  • Implied preemption - There are three possibilities:
    • When the local ordinance prohibits an act permitted by the state legislature
    • When a local ordinance permits an act prohibited by the state legislature
    • When there is clear legislative intent that the "field" is preempted by state law
      • The "field" is usually defined as when there is an extensive scope of state regulation which reflects a state intent to preempt all local regulations that are in a particular area. 
      • Occupation of the field is likely to be found when state law addresses an area that has traditionally been a matter of the state (eg: mortgage foreclosure process).

Implied preemption can be a controversial doctrine because this preemption may be significantly harder to prevent than either outright or express preemption. As such, some states have outlawed implied preemption. Further, if a state specifically authorizes an action, then the local government typically cannot restrict the action.

The state’s power to preempt the local government depends on multiple factors. The home rule applies when the state grants the local municipalities the power to govern locally. Also, for jurisdictions that follow Dillon’s Rule, the local municipalities can legislate only in areas where the state has explicitly allowed the local government. Allied Vending Co. v. Bowie court came up with a seven-part test to determine whether the state legislature has preempted a particular field by implication.

  1. Whether the enactment of the state law occurred prior to or after the local law regarding the same subject matter
  2. Whether the statute allows pervasive administrative regulations
  3. Whether the ordinance in question regulates the area of traditionally local matter
  4. Whether the state explicitly allows concurrent authority
  5. Whether the state agency administering and enforcing the law recognizes legal authority to act in such a way
  6. Whether the state legislative authority addresses the field in which the law attempts to regulate
  7. Whether the regulatory process regarding both local and state regulation would give rise to chaos and confusion without the preemption of the local law

Finally, there are instances where the local ordinance preempts state law. For example, City of Riverside v. Island Empire Patients Health and Wellness Center Inc. ruled that if the state statute does not explicitly forbid the ordinance, and if there is significant interest for the locality, then the court will favor the local ordinance over that of the state preemption.

[Last updated in March of 2024 by the Wex Definitions Team]