Two U.S. airlines announced Wednesday (July 22) passengers without a mask - won't be allowed to fly.
Southwest Airlines and American Airlines say the only exception will be for children under the age of two.
They're the toughest policies yet from U.S. airlines grappling with the global health crisis.
United has also announced a similar policy but appears to allow for some exemptions.
Until now most airlines have exempted passengers with medical conditions, though United and Delta require that any conditions be cleared before flying.
But Southwest will no longer allow medical or disability exemptions and said if anyone is unable to wear a face covering for any reason, it quote "regrets that we will be unable to transport the individual."
Passengers can remove their face coverings to eat, drink or take medicine, but those periods are expected to be very brief.
The new orders come as airlines grapple with how to restore travel demand.
American Airlines' mandate, which goes into effect July 29, will require customers above the age of two to also wear a mask from the time they enter their departure airport to the time they exit their arrival airport.
It added that customers who refuse to comply with the new policy may be barred from future travel with the airline for the duration of its face covering requirement.
Questions remain about what would happen if someone was turned away from a flight and what agency would be responsible.