A more thorough explanation:

Definition: Federal preemption is a principle in constitutional law that allows federal laws to override or replace any state laws or regulations that are inconsistent with them. This principle is derived from the Supremacy Clause of the U.S. Constitution.

Examples:

• If a state law conflicts with a federal law, the federal law takes precedence. For example, if a state law allows the use of a certain drug that is prohibited by federal law, the federal law would preempt the state law.
• The Garmon preemption doctrine prohibits state and local regulation of activities that are protected or prohibited by the National Labor Relations Act. For example, if a state law interferes with the right of employees to organize and bargain collectively, it would be preempted by federal law.
• The Machinists preemption doctrine prohibits state regulation of areas of labor activity or management-union relations that Congress has intentionally left unregulated. For example, if a state law attempts to regulate the collective bargaining process between employers and unions, it would be preempted by federal law.

These examples illustrate how federal preemption can limit the power of state governments to regulate certain areas of activity. It ensures that federal laws take precedence over conflicting state laws, which helps to promote consistency and uniformity in the application of laws across the country.