Federal supremacy and preemption refers to the idea that all state and local laws must not conflict with federal law.  The federal law is considered the supreme law and it always supersedes the state or local law.

The Constitution’s Article VI covers subjects such as:

• outstanding debt,
• prohibition of religious tests for office, and
• federal law’s power over state law.

Article VI’s first clause reassured creditors of the United States that they would be paid by the new government formed under the Constitution.  The third clause ensured that the government of the country would be secular and office holders at all levels of government would swear loyalty to the Constitution.  The second clause makes the Constitution, laws passed by Congress and treaties of the United States the supreme law of the land.  This has become known as the Supremacy Clause.  It has the most continuing effect to the modern day.

The Supremacy Clause establishes federal law as the highest form of law in the United States legal system.  It requires the state judges to defer to federal law even if state laws or constitutions conflict.  The Constitution mandates that “This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the contrary notwithstanding.”

When Congress passes a law within its constitutional authority, the state law must defer.  State constitutions are subordinate to federal statutes and treaties.  This constitutional requirement is called preemption.

The Supreme Court must decide if a state law comports with the policy set out in federal law, when the state law is challenged as unconstitutional based upon the Supremacy Clause.  The decision is affected by the manner in which Congress addressed the subject matter in relation to the States.  Congress may address this in either one of three ways such as:

•        Provide for exclusive federal control.

If Congress expresses in the law that it intends to control a specific subject matter and that subject matter is within the authority granted in Article I, then state law in that area is preempted.

•        Provide for concurrent federal-state jurisdiction.

Congress may determine that a subject is appropriate for both federal and State regulation, and expressly provide for concurrent jurisdiction in the law.

•        Remain silent regarding jurisdiction.

If Congress has not stated its preference, the Supreme Court may decide if the subject matter is under the exclusive control of the federal government.

The only way to effectively overcome federal supremacy is to demonstrate that the federal law is in itself unconstitutional, and therefore illegal.  In such cases, the federal law would be struck down by the court, and the state law would be the authority.