Delta Air Lines and Aeroméxico have sued the US government, challenging an order that will force them to unwind their immunised joint venture partnership by January 1, 2026.

The companies filed a suit at the 11th Circuit Court of Appeals. It seeks to overturn the US Department of Transportation (DOT) decision issued on September 15. In a statement provided to Reuters, Delta said that the petition “is our only option at this point in time and procedurally the next step in the process to protect Delta’s and Aeromexico’s business interests, global networks, and customers.”

Meanwhile, Aeroméxico said taking this decision “to request a review of the Department of Transportation’s final order has not been taken lightly,” adding that both companies “are inextricably a single entity in the cross-border market, operating for the benefit of consumers.”

The US carrier added that unwinding the venture by January 2026 “would be operationally and financially burdensome.” Both companies plan to ask the court for a stay to prevent enforcement of this deadline, pending the outcome of the court’s review.

Last month, the DOT found Aeroméxico and Delta’s joint venture to be anticompetitive and terminated the approval and antitrust immunity granted to the partnership. The US regulator claimed that the Mexican government distorted the market with its actions impacting slots at México City International, including banning all-cargo operations and implementing a slot regime that allegedly does not meet international standards. It argued this was an “arbitrary action,” while the Mexican government contended that the moves were to alleviate congestion at the airport.

The carriers received the antitrust immunity in November 2016, contingent on slots at Mexico City being made available to other carriers to boost competition.

ch-aviation schedule data shows Aeroméxico and Delta hold over 50% market share at Mexico City International by capacity. However, data from the transborder market in August 2025 shows the companies jointly carry 20.1% of the passengers between Mexico and the United States, while competitors Volaris, American Airlines, and United Airlines hold 17.3%, 17.2%, and 15.5% shares respectively.

If the joint venture is wound down in January 2026, both companies will still be able to continue their partnership through arms-length activities such as code sharing, marketing, and frequent flyer cooperation. In addition, Delta will be able to retain its 20% stake in Aeroméxico.