Aeromexico is appealing a US order to break up its partnership with Delta by January 1. The DOT says their joint venture is anticompetitive, controlling 60% of Mexico City-US flights. Aeromexico argues the split will cause concrete financial and operational harm, while Delta claims this could cancel routes and cost consumers $800M in benefits annually. The DOT sees issues like higher fares and less competition. American Airlines holds a similar market share, raising questions about broader impacts on the US-Mexico airline market.