United Airlines has asked the feds to block an effort by American Airlines to change its proposal for new service to China.
United says American's recent request to add a Chicago stopover on its proposed Dallas-Fort Worth International Airport-to-Beijing flights broke Transportation Department rules.
United, Fort Worth-based American, Northwest Airlines and Houston-based Continental Airlines submitted bids before a deadline in October.
But American has now asked to change its plan because a direct DFW-to-Beijing flight would violate limits on working hours in its contract with pilots.
The Transportation Department is expected to award the new China route in the next few weeks.
Other airlines had until yesterday to respond to American's updated proposal, which Northwest says should be rejected.
American is expected to respond by tomorrow.