United Airlines, one of the first American companies to have imposed a Covid-19 vaccine mandate for its staff, announced Thursday it will allow employees who have been granted an exemption to return to work.

The move came as the US government extended its mask mandate on public transportation for another month till April 18.

United had given its pilots, flight attendants and ground staff until the end of last September to upload proof of their vaccination or request an exemption for religious or medical reasons.

The group ended up laying off more than 200 employees and granting about 2,200 exemptions to employees who were given positions away from customers, though some decided to take unpaid leave.

"We plan to welcome back those employees who have been out... to their normal positions starting on Monday, March 28," the company said in a message to staff seen by AFP.

"Of course, if another variant emerges or the Covid trends suddenly reverse course, we will reevaluate the appropriate safety protocols at that time."

The extension of the transportation mask mandate announced by the Centers for Disease Control and Prevention will affect airplanes, buses, subways and ferries, and the agency noted in a statement they'll use the time to determine where masks should be mandatory going forward.

A growing number of US states are easing or dropping masking requirements in enclosed spaces.

The CDC broadly relaxed its recommendations on mask use in late February, and is no longer recommending wearing them indoors for the majority of American