The age-old parking-enforcement practice of tire-chalking is unconstitutional, a federal appeals court in Cincinnati ruled Monday, saying that it violated the Fourth Amendment's prohibition of unreasonable searches.

A three-judge panel of the 6th U.S. Circuit Court of Appeals, in a first-of-its-kind decision, ruled that marking a car's tires to gather information is a form of trespass requiring a warrant, similar to police attaching a GPS to a vehicle to track a suspected drug dealer.

Parking attendants across the country have been chalking tires with big white lines for decades in zones without meters to enforce time limits and issue tickets. It's a substantial source of revenue for many cities.

The decision, while undoubtedly bringing joy to parking scofflaws everywhere, could cost some cities money, either from lost revenue or having to install more meters.

On the other hand, as Fourth Amendment expert Orin Kerr of the University of Southern California law school tweeted, it "seems easy enough these days for parking enforcers to just take a photo of the car, or even just a close-up photo of the tire, rather than chalk it. ... No 4A issues then."

The 6th Circuit covers Ohio, Kentucky, Michigan and Tennessee. The case came from Saginaw, Michigan, where lawyer Philip Ellison engaged in a Facebook rant in 2016 after his law partner, sitting in his chalked car, got ticketed as the two talked by phone.

Ellison said a friend, Alison Taylor, saw the Facebook post and got in touch to complain about receiving her 15th $15 ticket in two years for parking for more than two hours downtown where there are no meters. Taylor, as the plaintiff, and Ellison, as her attorney, filed a civil-rights suit against Saginaw and a named parking-enforcement officer who Ellison claims "issues more than 95 percent of the tickets."

"We made a federal case out of tire-chalking," Ellison said. He acknowledged some surprise at his victory, as he could find no comparable chalking precedents.

The Fourth Amendment to the U.S. Constitution bars "unreasonable searches." U.S. District Judge Thomas Ludington in Bay City, Michigan, had dismissed the lawsuit, calling Ellison's legal theory "unorthodox" and concluding that chalking, although it is a type of search, is not at all unreasonable.

People have a lesser expectation of privacy in their vehicles than, for example, in their homes, Ludington wrote. Plus, he noted that the U.S. Supreme Court has carved out a "community caretaker" exception to warrant requirements for routine parking and traffic enforcement so that police can control the hazards of clogged streets.

Appeals court Judge Bernice Bouie Donald, writing for the unanimous three-judge panel, reversed Ludington's decision.

She said that traditional law regarding searches of vehicles had been upended by the Supreme Court's 2012 decision restricting the powers of police to use GPS devices to track criminal suspects.

Donald said the chalking of Taylor's car was just like the GPS installation, a trespass for the purpose of gathering incriminating information, and therefore it was a Fourth Amendment violation when conducted without a warrant.

She dismissed the "caretaker" exception, saying that Taylor's vehicle posed no safety risk. The city was trying to raise revenue, not "mitigate [a] public hazard," she wrote.

Ellison wants Ludington to certify the lawsuit as a class-action, with refunds for people who got tickets. He said Saginaw has been collecting up to $200,000 a year with parking tickets from tire marking.

An attorney for Saginaw did not immediately respond to a request for comment.

Information from The Associated Press was included in this story.