Petitioner's wife was killed in a boating accident when she fell overboard and was struck by the propeller of an outboard motor manufactured by Mercury Marine, a division of Brunswick Corporation. Her husband brought a products liability action in Illinois state court, asserting that the motor was unreasonably dangerous because it was not protected by a propeller guard. The trial court dismissed the complaint and the Illinois Supreme Court affirmed, holding that the tort suit was preempted by the Federal Boat Safety Act of 1971.

Under the statute, the Coast Guard promulgates regulations establishing safety standards for recreational vessels, and no State may enforce "a law or regulation" not identical to the federal regulation. The Coast Guard in 1990 decided against requiring propeller guards.

AAJ filed an amicus brief arguing that congressional preemption of "a law or regulation" of a State includes positive law (legislation or administrative regulations), but does not encompass the State's common law of torts.

The Supreme Court reversed. Writing for a unanimous Court, Justice John Paul Stevens construed the plain text of the statute's express preemption provision to include the positive law of a state, not common law tort actions. The Court also found no implied preemption. Congress did not intend to preempt the field of boating safety. Nor does plaintiff's lawsuit conflict with the Coast Guard's 1990 decision, which did not amount to a policy decision that neither federal nor state authorities should require propeller guards.