The Supreme Court struck down a Los Angeles ordinance Monday that allowed police to inspect hotel guest records on demand.
The justices voted 5-4 to reject the city's argument that the measure was needed to help fight prostitution, drug trafficking and illegal gambling at budget hotels and motels.
Los Angeles said that people engaging in those activities are less likely to use hotels if they know the facilities must collect guest information and turn it over at a moment's notice.
But Justice Sonia Sotomayor said for the court that the law is unconstitutional because it penalizes the hotel owners if they don't comply. "A hotel owner who refuses to give an officer access to his or her registry can be arrested on the spot," Sotomayor wrote. Business owners must at least be given a chance to object to a judge, she said.
Justice Anthony Kennedy and Sotomayor's three liberal colleagues joined her in the majority.
In dissent, Justice Antonin Scalia said the law "is eminently reasonable" given the use of cheap motels as places to stash migrants who have been smuggled across the border and as rendezvous points for child sex workers and their clients.
"The warrantless inspection requirement provides a necessary incentive for motels to maintain their registers thoroughly and accurately: They never know when law enforcement might drop by to inspect," Scalia said. Chief Justice John Roberts and Justices Samuel Alito and Clarence Thomas also dissented.
The federal appeals court in San Francisco divided 7-4 in ruling that the ordinance violates the privacy rights of the hotels, but not their guests.
Courts in other parts of the country have upheld similar laws.
Los Angeles requires hotels and motels to record basic information about guests and their vehicles. Guests without reservations, those who pay in cash and those who rent a room for less than 12 hours must also present photo identification at check in.
Nothing in the court's ruling on Monday affects the record-keeping requirements.
The case is Los Angeles v. Patel, 13-1175.
