The contract in Mr. Byrd’s case, from Budget, was typical. It said that “the only ones permitted to drive the vehicle other than the renter are the renter’s spouse, the renter’s co-employee (with the renter’s permission, on company business) or a person who appears at the time of the rental and signs an additional driver form.”

Mr. Byrd was none of those. But he testified that he and the woman who rented the car, Latasha Reed, had been together for 17 years, had five children and were engaged to be married.

In rejecting Mr. Byrd’s appeal, the United States Court of Appeals for the Third Circuit, in Philadelphia, acknowledged that federal appeals courts have differed about “whether the sole occupant of a rental vehicle has a Fourth Amendment expectation of privacy when that occupant is not named in the rental agreement.” The Third Circuit’s own precedents, the court said, “determined such a person has no expectation of privacy and therefore no standing to challenge a search of the vehicle.”

Mr. Byrd’s lawyers said this ignored reality. “Widespread noncompliance with authorized-driver provisions is an open secret,” they wrote, which is why rental agreements “often specify that the renter will carry greater risk of loss when an unlisted driver operates the vehicle.”

The Supreme Court’s decision in the case, Byrd v. United States, No. 16-1371, is very likely to have an outsize effect on black and Hispanic drivers, according to a brief from the American Civil Liberties Union and the National Association of Criminal Defense Lawyers.

Poor people rent a lot of cars. “There is a commonly held misconception that car rental is a luxury reserved for the wealthiest individuals,” a 2010 tax study found, noting that “more car rentals occur at neighborhood locations than at airport locations.”

“African-Americans generate over four times as many retail rental transactions as otherwise comparable Caucasians,” the study said. Other reports have demonstrated that black drivers are more likely than white ones to be pulled over by the police and more likely to be searched during the stop.