United Airlines (UAL) told workers on Wednesday that if they are unvaccinated against COVID-19 and are under an exemption for a religious or medical reason, they must take temporary leave starting in October.

United said the reason for the leave was the recent surge in COVID cases as the Delta variant causes a spike in infections across the globe, according to CNBC.

In a memo obtained by the Washington Post, Kirk Limacher, United’s vice president of human resources, said, “Given the dire statistics ... we 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.”

Those on a religious exemption will be placed on voluntary unpaid leave, while those on a medical exemption will be put on temporary medical leave, the Post said. Both temporary leaves begin on Oct. 2.

The airline announced in August that all 67,000 employees of its U.S. workforce would be required to be vaccinated against COVID-19 by Oct. 25. United said at the time that it would consider exemptions for religious and medical reasons.

In the notice to employees, United said that if an employee’s religious exemption is denied by the airline, they will have five weeks to be vaccinated with their first dose to be administered by Sept. 27 or be terminated, CNBC reported.

United said pilots, flight attendants, gate agents and airport customer service agents who are granted exemptions can return to work “once the pandemic meaningfully recedes.” No specific timeframe was provided.

Other staff such as mechanics and dispatchers will be able to return to work when new testing and other measures are put in place. Office personnel are still to be determed if they need to come in at all, United said.

The news of the unpaid leave from United comes as airlines such as Delta, American Airlines, and Alaska Airlines have said that they will end pay protection for their workers that contract COVID-19 or are exposed to the virus while on the job.

Delta has also implemented a $200 surcharge for unvaccinated employees on healthcare premiums from the company as a motivator to encourage workers to get vaccinated without imposing a vaccine mandate on its staff.

Frontier and Hawaiian Airlines also require their employees to be fully vaccinated against COVID-19.

As of Thursday premarket hours, shares of United were trading at $45.20, down 33 cents, or 0.72%.

united airlines A United Airlines aircraft is pictured. Photo: AFP / Daniel SLIM