American Airlines has joined fellow carriers United and Hawaiian in sending federally required notices of potential layoffs, Reuters is reporting .

American is warning up to 13,000 employees that their jobs are at risk unless the industry receives a third stimulus package that includes government grants and loans. Previously, airlines were the beneficiary of $25 billion in March 2020 in the initial CARES Act approved by Congress and $15 billion in December after passage of the second bill.

But both relief bills came with the stipulation that airlines not furlough any employees – for six months, or until Sept. 30, 2020, with the first bill and three months, or until March 30, 2021, with the second bill.

When the latest stipulations expire, employees at American, United and Hawaiian could be at risk.

Both American and United, which laid off a combined 32,000 workers starting in October, rehired most of their employees when the second relief bill was passed. But with the coronavirus still at a peak and travel restrictions still in place, both airlines quickly found that they had too many workers and not enough jobs .

"We are nearly five weeks into 2021, and unfortunately, we find ourselves in a situation similar to much of 2020," Chief Executive Doug Parker and President Robert Isom said in a memo to employees which was also included in a regulatory filing. "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.”

Reuters said American's potential furloughs include 1,850 pilots and 4,245 flight attendants. United's pilots approved a deal late last year to prevent furloughs until June.