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4.4 Preemption: The Supremacy Clause

Learning Objectives

  1. Understand the role of the supremacy clause in the balance between state and federal power.
  2. Give examples of cases where state legislation is preempted by federal law and cases where state legislation is not preempted by federal law.

When Congress does use its power under the commerce clause, it can expressly state that it wishes to have exclusive regulatory authority. For example, when Congress determined in the 1950s to promote nuclear power (“atoms for peace”), it set up the Nuclear Regulatory Commission and provided a limitation of liability for nuclear power plants in case of a nuclear accident. The states were expressly told to stay out of the business of regulating nuclear power or the movement of nuclear materials. Thus Rochester, Minnesota, or Berkeley, California, could declare itself a nuclear-free zone, but the federal government would have preempted such legislation. If Michigan wished to set safety standards at Detroit Edison’s Fermi II nuclear reactor that were more stringent than the federal Nuclear Regulatory Commission’s standards, Michigan’s standards would be preempted and thus be void.

Even where Congress does not expressly preempt state action, such action may be impliedly pre-empted. States cannot constitutionally pass laws that interfere with the accomplishment of the purposes of the federal law. Suppose, for example, that Congress passes a comprehensive law that sets standards for foreign vessels to enter the navigable waters and ports of the United States. If a state creates a law that sets standards that conflict with the federal law or sets standards so burdensome that they interfere with federal law, the doctrine of preemption will (in accordance with the supremacy clause) void the state law or whatever parts of it are inconsistent with federal law.

But Congress can allow what might appear to be inconsistencies; the existence of federal statutory standards does not always mean that local and state standards cannot be more stringent. If California wants cleaner air or water than other states, it can set stricter standards—nothing in the Clean Water Act or Clean Air Act forbids the state from setting stricter pollution standards. As the auto industry well knows, California has set stricter standards for auto emissions. Since the 1980s, most automakers have made both a federal car and a California car, because federal Clean Air Act emissions restrictions do not preempt more rigorous state standards.

Large industries and companies actually prefer regulation at the national level. It is easier for a large company or industry association to lobby in Washington, DC, than to lobby in fifty different states. Accordingly, industry often asks Congress to put preemptive language into its statutes. The tobacco industry is a case in point.

The cigarette warning legislation of the 1960s (where the federal government required warning labels on cigarette packages) effectively preempted state negligence claims based on failure to warn. When the family of a lifetime smoker who had died sued in New Jersey court, one cause of action was the company’s failure to warn of the dangers of its product. The Supreme Court reversed the jury’s award based on the federal preemption of failure to warn claims under state law.Cippolone v. Liggett Group, 505 US 504 (1993).

The Supremacy Clause

Article VI

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.

The preemptionBased on the supremacy clause, the preemption doctrine holds that state and federal laws that conflict must yield to the superior law, which is federal law. doctrine derives from the supremacy clause of the Constitution, which states that the “Constitution and the Laws of the United States…shall be the supreme Law of the Land…any Thing in the Constitutions or Laws of any State to the Contrary notwithstanding.” This means of course, that any federal law—even a regulation of a federal agency—would control over any conflicting state law.

Preemption can be either express or implied. When Congress chooses to expressly preempt state law, the only question for courts becomes determining whether the challenged state law is one that the federal law is intended to preempt. Implied preemption presents more difficult issues. The court has to look beyond the express language of federal statutes to determine whether Congress has “occupied the field” in which the state is attempting to regulate, or whether a state law directly conflicts with federal law, or whether enforcement of the state law might frustrate federal purposes.

Federal “occupation of the field” occurs, according to the court in Pennsylvania v. Nelson (1956), when there is “no room” left for state regulation. Courts are to look to the pervasiveness of the federal scheme of regulation, the federal interest at stake, and the danger of frustration of federal goals in making the determination as to whether a challenged state law can stand.

In Silkwood v. Kerr-McGee (1984), the court, voting 5–4, found that a $10 million punitive damages award (in a case litigated by famed attorney Gerry Spence) against a nuclear power plant was not impliedly preempted by federal law. Even though the court had recently held that state regulation of the safety aspects of a federally licensed nuclear power plant was preempted, the court drew a different conclusion with respect to Congress’s desire to displace state tort law—even though the tort actions might be premised on a violation of federal safety regulations.

Cipollone v. Liggett Group (1993) was a closely watched case concerning the extent of an express preemption provision in two cigarette labeling laws of the 1960s. The case was a wrongful death action brought against tobacco companies on behalf of Rose Cipollone, a lung cancer victim who had started smoking cigarette in the 1940s. The court considered the preemptive effect on state law of a provision that stated, “No requirement based on smoking and health shall be imposed under state law with respect to the advertising and promotion of cigarettes.” The court concluded that several types of state tort actions were preempted by the provision but allowed other types to go forward.

Key Takeaway

In cases of conflicts between state and federal law, federal law will preempt (or control) state law because of the supremacy clause. Preemption can be express or implied. In cases where preemption is implied, the court usually finds that compliance with both state and federal law is not possible or that a federal regulatory scheme is comprehensive (i.e., “occupies the field”) and should not be modified by state actions.


  1. For many years, the United States engaged in discussions with friendly nations as to the reciprocal use of ports and harbors. These discussions led to various multilateral agreements between the nations as to the configuration of oceangoing vessels and how they would be piloted. At the same time, concern over oil spills in Puget Sound led the state of Washington to impose fairly strict standards on oil tankers and requirements for the training of oil tanker pilots. In addition, Washington’s state law imposed many other requirements that went above and beyond agreed-upon requirements in the international agreements negotiated by the federal government. Are the Washington state requirements preempted by federal law?
  2. The Federal Arbitration Act of 1925 requires that all contracts for arbitration be treated as any other contract at common law. Suppose that the state of Alabama wishes to protect its citizens from a variety of arbitration provisions that they might enter into unknowingly. Thus the legislation provides that all predispute arbitration clauses be in bold print, that they be of twelve-point font or larger, that they be clearly placed within the first two pages of any contract, and that they have a separate signature line where the customer, client, or patient acknowledges having read, understood, and signed the arbitration clause in addition to any other signatures required on the contract. The legislation does preserve the right of consumers to litigate in the event of a dispute arising with the product or service provider; that is, with this legislation, consumers will not unknowingly waive their right to a trial at common law. Is the Alabama law preempted by the Federal Arbitration Act?