American Airlines has filed a federal lawsuit against the City of Chicago, claiming a breach of contract over gate space allocation at O’Hare International Airport. The complaint, filed Friday in the U.S. District Court for the Northern District of Illinois, centers on the city’s alleged favoritism toward United Airlines in its decision to reassign gate space—an action American says violates a binding agreement.

The lawsuit alleges that the City of Chicago, under the influence of United Airlines, intends to move forward with a gate space redetermination process this year that would grant United five additional gates while American stands to lose approximately four. This action, American asserts, contravenes the terms of a 2018 airline use and lease agreement signed by the City, American Airlines, and other carriers. That agreement laid the foundation for multibillion-dollar improvements at O’Hare and was designed to ensure fair gate distribution among all airlines.

“American Airlines sues Chicago O’Hare gate space” dispute stems from the city’s alleged premature attempt to alter gate assignments, despite specific provisions in the agreement that prohibit such changes during the current “gate space ramp-up period.” According to American, this period began in March 2025 when the final of three new gates at Terminal 3 became operational. Under the agreement, no gate redetermination is permitted until April 1, 2027.

American Airlines argues that proceeding with the redetermination this year would deprive the airline of its rightful opportunity to utilize the newly constructed gates, putting it at a competitive disadvantage. The airline also asserts that United has long sought to become the sole hub carrier at O’Hare, undermining the current dual-hub structure that supports both United and American.

“Defendants, at United’s request, now want to proceed with the gate redetermination this year while the ramp-up period has only just begun, depriving American of its opportunity to earn its fair share of gates,” the company stated in the filing.

The lawsuit also names Tracey Payne, the acting commissioner of Chicago’s Department of Aviation, and accuses the City of violating both the contract and its duty of good faith and fair dealing. American is seeking an injunction to stop the gate redetermination process and maintain its current gate access.

The legal action is titled American Airlines Inc. v. The City of Chicago et al., case number 1:25-cv-04874.

American Airlines is represented by Sean Berkowitz, Garrett S. Long, and David C. Tolley of Latham & Watkins LLP.

No immediate comments were available from representatives of the City of Chicago or United Airlines.