WASHINGTON — Supreme Court justices unanimously ruled Wednesday against a Minnesota rabbi whose frequent complaints about an airline got him tossed out of its frequent-flier program.

The court dismissed a lawsuit from Rabbi Binyomin Ginsberg over Northwest Airlines’ decision to strip him of his top-level frequent-flier status and then end his membership.

Northwest, since absorbed by Delta Air Lines, said it cut off Ginsberg because he complained too much. The rabbi said Northwest did not act in good faith and was trying to cut costs because of its merger with Delta.

In the 9-0 ruling, the court held that the Airline Deregulation Act of 1978 protects air carriers against such suits. The law was drafted to make the airlines more competitive, and in doing so, it shielded them from state laws and regulations that could affect their pricing or dictate how they deliver service. As a result, the court found, the law gives airlines the authority to boot customers from their frequent-flier programs at will.

The court also reasoned that passengers like Ginsberg can seek relief from the Department of Transportation, which has the authority to investigate frequent-flier programs. Or, said the opinion, written by Justice Samuel Alito Jr., passengers “can avoid an airline with a poor reputation and possibly enroll in a more favorable rival program.”

Ginsberg and his wife flew almost exclusively on Northwest, logging roughly 75 flights a year to travel across the U.S. and abroad to give lectures and take part in conferences on education and administration.

He said he flew on Northwest even when other airlines offered comparable or better flights and in 2005, reached the highest level of the WorldPerks program, Platinum Elite.

Northwest cut him off in 2008, shortly after Northwest and Delta agreed to merge. Ginsberg said Northwest was looking to get rid of the high-mileage customers.

Northwest says Ginsberg complained 24 times in seven months, including nine instances of luggage that turned up late on airport-baggage carousels. Northwest said that before it took action, it awarded Ginsberg $1,925 in travel-credit vouchers, 78,500 bonus miles, a voucher for his son and $491 in cash reimbursements.

The airline pointed to a provision of the mileage program’s terms that gives Northwest the right to cancel members’ accounts for abuse.

Material from the Tribune Washington Bureau is included in this report.