A lawsuit filed by several dozen travel agents accuses three of the nation’s biggest airlines of conspiring to raise prices for trips with multiple stops.

The suit filed in U.S. District Court in San Francisco accuses United, American and Delta Air Lines of conspiring to close a loophole that allowed travelers to save money by combining multiple one-way tickets for the same trip.

By closing the loophole, United, American and Delta can force travelers to book a single, multi-city ticket for hundreds and even thousands of dollars more than if they booked several one-way tickets separately. All three airlines announced the changes in April.

The airlines acknowledged that they have closed the loophole, saying many one-way fares are promotional offers, intended to serve specific routes, not to be combined with other routes. Representatives for the carriers said they did not confer with each other to close the loophole.


The lawsuit was filed Monday by 41 travel agents, who say they also represent their clients and others who were harmed by the pricing policy change.

The lawsuit accuses the airlines of violating federal and state antitrust laws. The lead attorney in the suit, Joseph Alioto of San Francisco, specializes in antitrust lawsuits and has opposed several airline mergers.

“The intent, purpose and effect of the conspiracy was and is to fix, raise, maintain, and or stabilize prices for air passenger transportation services on multi-city trips within the United States,” the lawsuit says.

American Airlines spokesman Casey Norton said the accusations are baseless. The airline made the “unilateral change to our fare rules to ensure that new lower fares we introduced would be available to passengers flying the route for which the fares were intended.”


In a statement, United Airlines said it also made the change on its own to keep travelers from combining one-way flights, “resulting in prices that were different than what United intended for the connecting itinerary.”

Representatives for Delta could not be reached for comment.

To read more about travel, tourism and the airline industry, follow Hugo Martin on Twitter at @hugomartin.