WASHINGTON — The Supreme Court ruled 6-3 on Wednesday that U.S. troops injured in combat zones may sue military contractors for negligence. The court held that neither federal law nor the Constitution shields military contractors if their mistakes or negligence result in soldiers being injured in a combat zone.

Justice Clarence Thomas wrote the majority opinion, joined by Justices Sonia Sotomayor, Elena Kagan, Neil M. Gorsuch, Amy Coney Barrett and Ketanji Brown Jackson. Justice Samuel A. Alito Jr. dissented along with Chief Justice John G. Roberts and Justice Brett M. Kavanaugh. Alito wrote in his dissent that because the Constitution gives the federal government exclusive authority over foreign affairs and the conduct of wars, federal law preempts all state law that substantially interferes with the federal government's exercise of those powers.

The ruling overturned a decision by the 4th Circuit Court of Appeals and allows a lawsuit brought by Winston Henceley against Fluor Corporation to proceed. A federal judge in South Carolina and the 4th Circuit had thrown out Henceley's suit. The 4th Circuit held that tort claims against private service contractors integrated into combatant activities over which the military retains command authority are preempted during wartime.

In 2016, Henceley was 20 years old when his skull was fractured and he suffered brain injuries that left him permanently disabled. He tried to stop and question Ahmad Nayeb, an Afghan employee, as Nayeb walked toward soldiers gathered for a Veteran's Day 5K race at Bagram Airfield. Nayeb, a Taliban operative working at the base, detonated a suicide bomb that killed five soldiers and wounded 17. The Army concluded that Henceley's intervention likely prevented a far greater tragedy.

The Army's investigation concluded that Fluor Corporation was primarily responsible for the attack. Its report said Fluor was negligent in hiring an Afghan who had been a Taliban operative and failed to closely supervise him.

The Trump administration joined the case in defense of Fluor. Its lawyers argued that allowing state-law tort suits would harm the separation of powers and the federal government's ability to prosecute wars.