A system scheduling error has left thousands of American Airlines flights in December without scheduled pilots.
The Allied Pilots Association estimated that more than 15,000 flights from 17 December to 31 December were affected by a glitch in the system in which pilots bid for time off based on seniority.
Spokesman for the Allied Pilots Association Dennis Tajer said: "Basically there's a crisis at American for manning the cockpits."
American Airlines spokesperson Matt Miller, said: "We have reserve pilots to help cover flying in December, and we are paying pilots who pick up certain open trips 150% of their hourly rate as much as we are allowed to pay them per the contract."
In an email to employees, American had offered pilots the extra pay to work certain flights over the Christmas period.
But the union filed a grievance, saying that some restrictions on overtime pay violated the group's contract, and that management had still not reached out to discuss how best to resolve the shortage.
"I'm watching a 'Grinch that stole Christmas' thing happening. And we don't want to see that happening for our passengers," Mr Tajer said.
American is hoping to avoid having to cancel flights, which, in addition to being a nuisance for travellers, could cost the carrier millions in lost revenue.
In the best-case scenario, labour costs for the quarter will likely climb as a result of pilots' higher pay on those flights, just months after a substantial mid-contract pay increase for pilots and flight attendants spooked investors and temporarily sent the carrier's shares tumbling.
