Don’t throw away those masks yet.

The U.S. Department of Justice today appealed a federal judge’s ruling that struck down the U.S. government’s mask-wearing mandate on airplanes and mass transit systems, with health officials insisting the requirement is still needed to protect against the spread of COVID-19.

The Monday ruling by U.S. District Judge Kathryn Kimball Mizelle in Florida prompted a lifting of mask-wearing requirements by major airlines, at airports and by most major transit systems in Los Angeles County and beyond. Mizelle ruled that the U.S. Centers for Disease Control and Prevention had exceeded its authority in issuing the mask-wearing mandate on transportation systems.

But on Wednesday, the CDC issued a statement saying it continues to believe that requiring masks in indoor transportation settings “remains necessary for the public health.”

“CDC will continue to monitor public health conditions to determine whether such an order remains necessary,” according to a statement from the agency. “CDC believes this is a lawful order, well within CDC’s legal authority to protect public health.”

Immediately after CDC issued the statement, the Department of Justice filed a notice of appeal in Florida.

There was no immediate word on whether the government would seek an emergency stay of Mizelle’s ruling, which would in effect put the mask mandate back in place pending the results of the appeal.   In the meantime, mask-wearing remains optional on major airlines. In the Southland, masks are no only strongly recommended—but not required—on most transportation systems.

The Los Angeles County Metropolitan Transportation Authority lifted the mandate on its buses and rail lines, as did the Orange County Transportation Authority and Metrolink. The Los Angeles Department of Transportation also scrapped the mandate on its DASH and Commuter Express buses.

Masks are now optional at Los Angeles International Airport, Hollywood Burbank Airport and John Wayne Airport in Orange County.

The ride-hailing services Uber and Lyft also dropped its mask mandates for drivers and passengers, saying face coverings are still recommended.

Mask mandates have slowly been lifted in many settings in recent weeks. Los Angeles County and the state have scrapped requirements for masks at outdoor and indoor mega-events, and face coverings are no longer mandatory inmost indoor environments.

Mask requirements inside school classrooms have also been lifted, and face coverings are now only strongly recommended at L.A. County campuses. Masks are also “strongly recommended,” but not required, on school buses.

The county still requires masks at health-care facilities.

Florida judge voids U.S. mask mandate for planes, other travel