The U.S. Supreme Court unanimously sided with Northwest Airlines, now part of Atlanta-based Delta Air Lines, in the case of a complaining rabbi who was booted from the company’s frequent flier program.

The Court said Wednesday that the Airline Deregulation Act gives airlines broad leeway in how they conduct their affairs, including frequent flier programs. Northwest’s frequent flier contract said it could terminate a flier’s account at its own “sole discretion.”

In this case, Northwest said Rabbi S. Binyomin Ginsberg, of Minneapolis, complained too much about service as a way to seek additional rewards, so the airline revoked his membership. Ginsberg said his complaints were polite and infrequent — according to court records, he complained 24 times over an eight-month period — and that Northwest was trying to dump his expensive account to look better in its recent merger with Delta.

The unanimous opinion was written by Justice Samuel Alito.

“Our holding also does not leave participants in frequent flyer programs without protection,” Alito wrote, noting that airline deregulation was intended to promote passenger interests “by allowing the free market to operate.”

“If an airline acquires a reputation for mistreating the participants in its frequent flyer program (who are generally the airline’s most loyal and valuable customers), customers can avoid that program and may be able to enroll in a more favorable rival program,” Alito wrote.

Ginsberg said in an interview that a jury of average Americans who have dealt with flying headaches would have sided with him.

“I believe this ruling has the potential of opening up the floodgates that the airlines will take advantage of and say, ‘We have something to hang our hat on. The Supreme Court ruled in our favor which means (airline deregulation) … allows us to do basically whatever we want,’ ” Ginsberg said.

Delta spokesman Paul Skrbec said in an email, “We’re pleased the Court found preemption under the federal Airline Deregulation Act. We’ll continue to provide customers with a loyalty program that offers valuable benefits and rewards our members’ travel.”

Northwest revoked Ginsberg’s WorldPerks membership and all of his frequent flier miles in 2008, and the case has wound through the courts ever since, as Northwest merged with Delta.

Ginsberg made his case through state contract law, saying the airline had broken common law of “good faith and fair dealing” by revoking his WorldPerks membership. But the 1978 Airline Deregulation Act did not allow states to enforce their own regulations on airlines, and the Court said this applied to common law as well.

Ginsberg’s attorney, Adina Rosenbaum of Public Citizen, pointed out that Alito’s opinion left the door open for some claims similar to Ginsberg’s “when they are an attempt to vindicate the parties’ implicit understanding of the contract. The court also recognized that plaintiffs in cases such as Rabbi Ginsberg’s might be able to vindicate their rights through breach-of-contract claims.”

The ruling also emphasizes that the federal Department of Transportation has oversight over unfair or deceptive airline practices.

Ginsberg said he flies more often now than in 2008, but the groups seeking him for speaking gigs on education and administration book the flights, so he’s not seeking out frequent flying perks.

He said he called Northwest to compliment them as much as he complained, and was always a courteous flier. The case is really about free speech and core American values, he said, adding: “I believe George Washington is not pleased with this decision.”