SAN FRANCISCO — A group of travel agents and passengers have filed an anti-trust lawsuit against American Airlines, Delta Airlines and United in the wake of the multi-city itinerary fare hike scandal.

The group alleges that the three airlines colluded in the scheme, removing their lowest non-refundable fares from multi-city itineraries, according reports.

The lawsuit noted that “each [of the airlines] announced their agreement in substantially identical terms in written notifications given to members of the travel agency industry.” Agents who found a loophole to circumvent the higher fares have received debit memos.