For an airline, taking off on time is crucial to maintain a good on-time performance rating. But in an effort to keep those numbers up, a pilots’ union says American Airlines is abdandoning thousands of standby passengers at the gate.

Dan Carey, president of the Allied Pilots Association, which represents pilots who fly for the airline, said Thursday that American left almost 20,000 passengers waiting to fly standby in February, because of its policy of closing the door from the gate area 10 minutes before scheduled departure.

“On almost 13,000 flights, standby passengers were denied boarding even though the aircraft had open seats,” he writes, calling it a “failure” that could have affected up to 16% of all American flights.

“This is intolerable,” Carey says.

While he recognizes that gate agents are also under a lot of pressure to get that jet bridge retracted and close the plane’s doors, Carey says pilots should do “everything possible to ensure that no passengers are left behind while seats are empty.”

He urges pilots to track standby passenger lists, and be “aggressively proactive” in defending standby passengers and fellow employees.

A spokesman for American tells Consumerist that the airline has policies and procedures in place to ensure standby passengers and employees are accommodated when there are open seats, and says the figures cited by APA are off.

“This internal report was created years ago to help us identify trends,” the spokesman told Consumerist. “It’s imprecise and not representative of reality because it includes the names of many people who are not physically present at the gate area during the boarding process. This and many other factors cause any reporting on unaccommodated passengers to be significantly inflated.”

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.