A technical glitch in American Airlines’ pilot scheduling system has left the Dallas/Fort Worth-based carrier without enough pilots during the upcoming holiday season, igniting a social media uproar when news of the situation became public.

According to the Allied Pilots Association (APA), the union representing American’s 15,000 pilots, the airline first disclosed the failure within the pilot schedule bidding system Nov. 24. APA said American issued an update Nov. 28 detailing “significant holes” in its operation, and according to a union statement, “unilaterally invoked a solution for crewing affected flights.”

Approximately 15,000 flights over the Dec. 17-31 period are affected, according to a union spokesperson, as reported by Dallas News.

American Airlines told ATW the carrier is “working diligently to address the issue and expects to avoid cancellations this holiday season. 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. We will work with the APA to take care of our pilots and ensure we get our customers to where they need to go over the holidays.”

APA said management’s actions violate the pilots’ contract terms and the union has filed a grievance. “Because management unilaterally created their solution in violation of the contract, neither APA nor the contract can guarantee the promised payment of the premium being offered,” APA said.