American Airlines will notify 13,000 workers that they could be laid off due the prolonged industry downturn caused by the COVID-19 pandemic, the carrier said Wednesday.

The airline expects to fly at least 45 percent less in the first quarter, American's executives said in a letter to employees, extending the industry slump as expectations for a travel recovery are delayed due to the slow rollout of coronavirus vaccines.

The letter, from the carrier's Chief Executive Doug Parker and President Robert Isom, said American no longer expects to be at full capacity this summer.

"The vaccine is not being distributed as quickly as any of us believed, and new restrictions on international travel that require customers to have a negative COVID-19 test have dampened demand," they said in the letter.

"Of course, this is not where we want to be, and we will work with union leadership to do everything we can to mitigate job impact as much as possible."

American furloughed 19,000 workers in October after a prior round of federal support expired, but brought the workers back after Congress enacted more federal support at the end of 2020.

Parker and Isom said they backed efforts by airline worker unions to win another round of support in Congress. The company also plans to establish new programs to encourage early retirement or voluntary furloughs.

American's announcement came after the United Airlines last week sent similar notices to 14,000 workers.