DENVER (CBS) – Thousands of American Airlines flights set to depart during the holiday season have no pilot scheduled to fly the aircraft, the Allied Pilots Association announced Wednesday.

The union called it a “scheduling failure.”

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“On Friday, management disclosed a failure within the pilot schedule bidding system. As a result, thousands of flights currently do not have pilots assigned to fly them during the upcoming critical holiday period,” the union stated.

A glitch in the scheduling system that allows employees to request time off based on seniority was responsible for the shortage of pilots for flights from Dec. 17-31, Reuters reported.

American Airlines has reportedly offered pilots extra pay to work certain flights in the busy holiday travel period.

However, the union filed a grievance, stating “management unilaterally created their solution in violation of the contract.”

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“Management’s actions likewise jeopardize any collaborative effort to ensure our passengers have a pilot crew to take them to their important holiday events,” union officials stated.

“Flights that are scheduled without a captain, first officer or both originate from Dallas-Fort Worth International, American’s largest hub, and airports in Boston, Miami, New York, Philadelphia, Salt Lake City and Charlotte, North Carolina, according to a company memo to the union,” Bloomberg News reports.

Officials with Denver International Airport told CBS4 American Airlines has not notified them of any potential issues with their service.

“Currently American Airlines operations are normal,” said Daria Serna.

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American Airlines is the largest U.S. carrier.