American is the world's biggest airline and has about 15,000 active pilots and expects to operate more than 200,000 flights in December, according to The Associated Press.
More than 15,000 upcoming American Airlines flights are now pilotless and face cancellation during the busy holiday travel rush unless the airline can resolve a scheduling issue that accidently gave too many pilots a Christmas vacation.
The discrepancy in the figures presented by the airline and the union exists because American is expecting numerous flights to be picked up by the reserve pilots mentioned in the airline's statement. American is one of three airlines that now provide flight service from the Greater Killeen-Fort Hood Regional Airport.
American has offered its pilots 150 percent of normal hourly pay to cover certain unstaffed flights.
APA represents the 15,000 pilots with American Airlines.
"This is a potential crisis that we see well in advance", said Dennis Tajer, a spokesman for the union.
The error has affected flights in major destinations, including Miami, Dallas-Fort Worth, Chicago's O'Hare and New York's LaGuardia Airport, according to CNBC. "The system went from responsibly scheduling everybody to becoming Santa Claus to everyone". But the union filed a grievance, saying that some restrictions on overtime pay violated the group's contract. Still, industry experts say the increased complexity of airline computer systems is to blame for a growing number of glitches that have recently grounded airplanes and posted ultra-cheap airfares.
The glitch caused the scheduling system to show that American had ample staffing coverage for some planned flights when it actually didn't, Miller said.
"We will work with the (union) to take care of our pilots and ensure we get our customers to where they need to go over the holidays". You want the days off?
"That data does not support management's statement regarding December flights that 'only a few hundred are now unassigned to pilots, ' " the union said.
The error, disclosed to employees on Friday and widely reported this week, was an "isolated incident" and a "mistake", Miller said.
Mr Tajer added: "I'm watching a 'Grinch that stole Christmas" thing happening.
"We are being told to expect business as usual", said Beardsley.