United Airlines revealed last month that it will require nearly all of its 67,000 US employees to be vaccinated against COVID-19 by October 25, or risk termination.

At the time, the airline said that certain religious and health exemptions would be made on a case-by-case basis.United Airlines employees who have been granted religious exemptions for the company’s recently-announced COVID-19 vaccine mandate will be forced to take a temporary, unpaid leave of absence beginning October 2, according to a memo issued to airline staffers this week.

Citing recent spikes in COVID-19 infections, hospitalizations and related deaths, the company stressed that it “can no longer allow unvaccinated people back into the workplace until we better understand how they might interact with our customers and their vaccinated coworkers.”

United Airlines did not specify a target date to lift the mandatory unpaid leave.

“Once the pandemic meaningfully recedes, you will be welcomed back to the team on active status, which may include other, safety-related workplace measures that do not exist today,” the memo stated. Employees who were denied approval for such accommodation are required to be fully vaccinated against COVID-19 within five weeks of the denial notice.

Unvaccinated employees who do not have an exemption and refuse to get their first shot by September 27 “will be separated from the company.”