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The City of Chicago has formally urged a federal judge in Illinois to permit United Airlines to intervene in an ongoing lawsuit filed by American Airlines challenging Chicago’s decision to reassign gate space at O’Hare International Airport. The city emphasized the “unique nature” of its airline use and lease agreement, which operates as a single contract between Chicago and all carriers, underscoring the importance of United’s involvement.

United Airlines has sought to join the suit, citing the potential impact on its economic interests and contractual relationship with the city. Chicago backed United’s bid in filings submitted this week, countering American Airlines’ narrow interpretation of the contract at the heart of the dispute.

American Airlines’ complaint, filed May 2, objects to the city’s move to reallocate gate assignments in a manner that would grant United five additional gates at O’Hare, enhancing its competitive position, while American risks losing approximately four gates. The airline argues this reassignment violates the terms of a 2018 multi-carrier airline use and lease agreement, which facilitated significant investments to upgrade O’Hare and ensured fair gate distribution.

However, Chicago maintains that the agreement is not exclusive to American and explained that the Federal Aviation Administration requires airports receiving federal funding to treat similarly situated airlines equitably through a unified contract signed by all participating carriers. This framework supports United’s right to intervene and challenges American’s position that the contract benefits only a single airline.

The city also highlighted that the annual gate space redetermination process must be applied collectively to all airlines, making it impractical to halt the process for American while advancing it for United.

“Allowing United Airlines to intervene is the more prudent approach,” the city stated, warning that separate lawsuits would strain city and judicial resources and could result in contradictory court orders affecting gate space determinations.

While Chicago and United both support the redetermination, the city stressed that their interests differ. Chicago prioritizes fair contract administration and the overall success of all airlines operating at O’Hare, whereas United seeks to advance its own growth strategy.

Legal representation in the case includes Sean Berkowitz, Garrett S. Long, and David C. Tolley for American Airlines; Cornel Hershel Kauffman, Fiona A. Burke, Peter J. Kirsch, and Samantha Caravello for the City of Chicago; and Gabor Balassa, Amarto Bhattacharyya, and Elisabeth Callaghan Logan for United Airlines.

The case, American Airlines Inc. v. The City of Chicago et al., case number 1:25-cv-04874, is pending in the U.S. District Court for the Northern District of Illinois.