Federal preemption

In the law of the United States, federal preemption is the invalidation of a U.S. state law that conflicts with federal law.

According to the Supremacy Clause (Article VI, clause 2) of the United States Constitution,

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, anything in the Constitution or laws of any State to the contrary notwithstanding.

As the Supreme Court stated in Altria Group v. Good, 555 U.S. 70 (2008), a federal law that conflicts with a state law will trump, or "preempt", that state law:

Consistent with that command, we have long recognized that state laws that conflict with federal law are "without effect." Maryland v. Louisiana, 451 U. S. 725, 746 (1981)

Although many concurrent powers are subject to federal preemption, some are usually not, such as the power to tax private citizens.

In Altria Group v. Good, the Court wrote:

When the text of a pre-emption clause is susceptible of more than one plausible reading, courts ordinarily "accept the reading that disfavors pre-emption." Bates v. Dow Agrosciences LLC, 544 U.S. 431, 449 (2005).

In Wyeth v. Levine (2009), the Court emphasized what it called the "two cornerstones" of pre-emption jurisprudence:

First, "the purpose of Congress is the ultimate touchstone in every pre-emption case." Medtronic, Inc. v. Lohr, 518 U. S. 470, 485 (1996) (internal quotation marks omitted); see Retail Clerks v. Schermerhorn, 375 U. S. 96, 103 (1963). [Medtronic: "[O]ur analysis of the scope of the statute's pre-emption is guided by our oft-repeated comment, initially made in Retail Clerks v. Schermerhorn, 375 U.S. 96, 103, ... (1963), that "the purpose of Congress is the ultimate touch-stone" in every pre-emption case."] Second, "[i]n all pre-emption cases, and particularly in those in which Congress has 'legislated … in a field which the States have traditionally occupied,' … we 'start with the assumption that the historic police powers of the States were not to be superseded by the Federal Act unless that was the clear and manifest purpose of Congress.' " Lohr, 518 U. S., at 485 (quoting Rice v. Santa Fe Elevator Corp., 331 U. S. 218, 230 (1947) ).

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