American Airlines said on Wednesday it will send furlough notices to 13,000 employees this week as second round of federal aid package ends next month.

“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,” American’s CEO Doug Parker and President Robert Isom wrote in a note to staff.

United Airlines has sent new furlough warnings to 14,000 workers, while Delta Air Lines and Southwest Airlines have prevented layoffs mainly through voluntary layoff programs.

Notices will be sent to 4,245 flight attendants, 3,145 fleet service workers, 1,850 pilots, 1,420 maintenance workers, 1,205 in passenger service, 100 dispatchers and 40 instructors.

“Obviously, issuing these required WARN notices isn’t a step we want to take,” Parker and Isom said. “Tens of thousands of our colleagues have faced extreme uncertainty about their job security over the past 12 months, and that’s on top of the emotional stress all of our team has faced during an incredibly difficult year.”

American offers early retirement programs for employees who have been in the company for more than 10 years, including up to $150,000 in health reimbursements and some travel benefits. It also introduces annual or 18-month leaves with partial remuneration.