The Supremacy Clause of the Constitution of the United States (Article VI, Clause 2), establishes that the Constitution, federal laws made pursuant to it, and treaties made under its authority, constitute the "supreme law of the land". It provides that state courts are bound by the supreme law; in case of conflict between federal and state law, the federal law must be applied. Even state constitutions are subordinate to federal law when that law is made in pursuance to the Constitution. In the same respect, the Supremacy Clause establishes that the States are NOT bound by laws created by the federal government that are not made under the specifically enumerated powers delegated to the federal government through the Constitution. "…the power of the Constitution predominates. Any thing, therefore, that shall be enacted by Congress contrary thereto, will not have the force of law." (James Wilson, Pennsylvania Ratifying Convention, 1787  ) "There is no position which depends on clearer principles, than that every act of a delegated authority, contrary to the tenor of the commission under which it is exercised, is void. No legislative act, therefore, contrary to the Constitution, can be valid." (Alexander Hamilton, Federalist #78  )
In essence, it is a conflict-of-laws rule specifying that certain federal acts take priority over any state acts that conflict with federal law, but when federal law conflicts with the Constitution that law is null and void. In this respect, the Supremacy Clause follows the lead of Article XIII of the Articles of Confederation, which provided that "Every State shall abide by the determination of the United States in Congress Assembled, on all questions which by this confederation are submitted to them." A constitutional provision announcing the supremacy of federal law, the Supremacy Clause assumes the underlying priority of federal authority, only when that authority is expressed in the Constitution itself. No matter what the federal government or the states might wish to do, they have to stay within the boundaries of the Constitution. This makes the Supremacy Clause the cornerstone of the whole American political structure.
In Madison's Notes of Debates in the Federal Convention of 1787, the Supremacy Clause is introduced as part of the New Jersey Plan. During the debate, it is first put up for a motion by Luther Martin on July 17th where it passed unanimously.
In Federalist No. 33, Alexander Hamilton writes about the Supremacy Clause that federal laws by definition must be supreme. If the laws do not function from that position then they amount to nothing, noting that "A law, by the very meaning of the term, includes supremacy. It is a rule which those to whom it is prescribed are bound to observe. This results from every political association. If individuals enter into a state of society, the laws of that society must be the supreme regulator of their conduct. If a number of political societies enter into a larger political society, the laws which the latter may enact, pursuant to the powers entrusted to it by its constitution, must necessarily be supreme over those societies, and the individuals of whom they are composed."
In Federalist No. 44, James Madison defends the Supremacy Clause as vital to the functioning of the nation. He noted that state legislatures were invested with all powers not specifically defined in the Constitution, but also said that having the federal government subservient to various state constitutions would be an inversion of the principles of government, concluding that if supremacy were not established "it would have seen the authority of the whole society everywhere subordinate to the authority of the parts; it would have seen a monster, in which the head was under the direction of the members".
The constitutional principle derived from the Supremacy Clause is federal preemption. Preemption applies regardless of whether the conflicting laws come from legislatures, courts, administrative agencies, or constitutions. For example, the Voting Rights Act of 1965, an act of Congress, preempts state constitutions, and Food and Drug Administration regulations may preempt state court judgments in cases involving prescription drugs.
Congress has preempted state regulation in many areas. In some cases, such as the 1976 Medical Device Regulation Act, Congress preempted all state regulation. In others, such as labels on prescription drugs, Congress allowed federal regulatory agencies to set federal minimum standards, but did not preempt state regulations imposing more stringent standards than those imposed by federal regulators. Where rules or regulations do not clearly state whether or not preemption should apply, the Supreme Court tries to follow lawmakers’ intent, and prefers interpretations that avoid preempting state laws.
Supreme Court interpretations
In Ware v. Hylton, 3 U.S. (3 Dall.) 199 (1796), the United States Supreme Court for the first time applied the Supremacy Clause to strike down a state statute. Virginia had passed a statute during the Revolutionary War allowing the state to confiscate debt payments by Virginia citizens to British creditors. The Supreme Court found that this Virginia statute was inconsistent with the Treaty of Paris with Britain, which protected the rights of British creditors. Relying on the Supremacy Clause, the Supreme Court held that the treaty superseded Virginia's statute, and that it was the duty of the courts to declare Virginia's statute "null and void".
In Marbury v. Madison, 5 U.S. 137 (1803), the Supreme Court held that Congress cannot pass laws that are contrary to the Constitution, and it is the role of the Judicial system to interpret what the Constitution permits. Citing the Supremacy Clause, the Court found Section 13 of the Judiciary Act of 1789 to be unconstitutional to the extent it purported to enlarge the original jurisdiction of the Supreme Court beyond that permitted by the Constitution.
In Martin v. Hunter's Lessee, 14 U.S. 304 (1816), and Cohens v. Virginia, 19 U.S. 264 (1821), the Supreme Court held that the Supremacy Clause and the judicial power granted in Article III give the Supreme Court the ultimate power to review state court decisions involving issues arising under the Constitution and laws of the United States. Therefore, the Supreme Court has the final say in matters involving federal law, including constitutional interpretation, and can overrule decisions by state courts.
In McCulloch v. Maryland, 17 U.S. (4 Wheat.) 316 (1819), the Supreme Court reviewed a tax levied by Maryland on the federally incorporated Bank of the United States. The Court found that if a state had the power to tax a federally incorporated institution, then the state effectively had the power to destroy the federal institution, thereby thwarting the intent and purpose of Congress. This would make the states superior to the federal government. The Court found that this would be inconsistent with the Supremacy Clause, which makes federal law superior to state law. The Court therefore held that Maryland's tax on the bank was unconstitutional because the tax violated the Supremacy Clause.
In Ableman v. Booth, 62 U.S. 506 (1859), the Supreme Court held that state courts cannot issue rulings that contradict the decisions of federal courts, citing the Supremacy Clause, and overturning a decision by the Supreme Court of Wisconsin. Specifically, the court found it was illegal for state officials to interfere with the work of U.S. Marshals enforcing the Fugitive Slave Act or to order the release of federal prisoners held for violation of that Act. The Supreme Court reasoned that because the Supremacy Clause established federal law as the law of the land, the Wisconsin courts could not nullify the judgments of a federal court. The Supreme Court held that under Article III of the Constitution, the federal courts have the final jurisdiction in all cases involving the Constitution and laws of the United States, and that the states therefore cannot interfere with federal court judgments.
In Pennsylvania v. Nelson, 350 U.S. 497 (1956) the Supreme Court struck down the Pennsylvania Sedition Act, which made advocating the forceful overthrow of the federal government a crime under Pennsylvania state law. The Supreme Court held that when federal interest in an area of law is sufficiently dominant, federal law must be assumed to preclude enforcement of state laws on the same subject; and a state law is not to be declared a help when state law goes farther than Congress has seen fit to go.
In Reid v. Covert, 354 U.S. 1 (1957), the Supreme Court held that international treaties and laws made pursuant to them must comply with the Constitution.
In Cooper v. Aaron, 358 U.S. 1 (1958), the Supreme Court rejected attempts by Arkansas to nullify the Court's school desegregation decision, Brown v. Board of Education. The state of Arkansas, acting on a theory of states' rights, had adopted several statutes designed to nullify the desegregation ruling. The Supreme Court relied on the Supremacy Clause to hold that the federal law controlled and could not be nullified by state statutes or officials.
In Edgar v. MITE Corp., 457 U.S. 624  (1982), the Supreme Court ruled: "A state statute is void to the extent that it actually conflicts with a valid Federal statute". In effect, this means that a State law will be found to violate the Supremacy Clause when either of the following two conditions (or both) exist:
In 1920, the Supreme Court applied the Supremacy Clause to international treaties, holding in the case of Missouri v. Holland, 252 U.S. 416, that the Federal government's ability to make treaties is supreme over any state concerns that such treaties might abrogate states' rights arising under the Tenth Amendment.
The Supreme Court has also held that only specific, "unmistakable" acts of Congress may be held to trigger the Supremacy Clause. Montana had imposed a 30 percent tax on most sub-bituminous coal mined there. The Commonwealth Edison Company and other utility companies argued, in part, that the Montana tax "frustrated" the broad goals of the federal energy policy. However, in the case of Commonwealth Edison Co. v. Montana, 453 U.S. 609  (1981), the Supreme Court disagreed. Any appeal to claims about "national policy", the Court said, were insufficient to overturn a state law under the Supremacy Clause unless "the nature of the regulated subject matter permits no other conclusion, or that the Congress has unmistakably so ordained".
However, in the case of California v. ARC America Corp., 490 U.S. 93  (1989), the Supreme Court held that if Congress expressly intended to act in an area, this would trigger the enforcement of the Supremacy Clause, and hence nullify the state action. The Supreme Court further found in Crosby v. National Foreign Trade Council, 530 U.S. 363  (2000), that even when a state law is not in direct conflict with a federal law, the state law could still be found unconstitutional under the Supremacy Clause if the "state law is an obstacle to the accomplishment and execution of Congress's full purposes and objectives". Congress need not expressly assert any preemption over state laws either, because Congress may implicitly assume this preemption under the Constitution.
- Federal preemption
- Intergovernmental immunity
- Necessary and Proper Clause
- States' rights
- Section 109 of the Constitution of Australia – analogous section of the Constitution of Australia
- Paramountcy (Canada) – analogous doctrine in Canadian constitutional law
- Primacy of European Union law – analogous doctrine in European Union law