The lawsuit claims the city of Chicago has breached the Airline Use and Lease Agreement and would give United Airlines five more gates, while taking away four gates from American Airlines.

After American Airlines filed a lawsuit Friday against the city of Chicago over the proposed re-allocation of gates at the airport, United Airlines President Brett Hart told employees today “we plan to take steps to protect our interests and utilize these new gates to benefit our customers.”

The new flights represent continued growth for American, which says it will offer 25% more seats on flights out of O’Hare this summer.