The boss of American airline Delta has said that over "100 people" have been have been blacklisted by the company over their refusal to wear face masks.
During an appearance on the Today Show, CEO Ed Bastian recently told passengers "If you insist on not wearing your mask, we will insist that you don't fly Delta."
Face coverings have been mandatory on Delta flights since the 1st of May. The company introduced the measure along with a decision to stop selling the middle seats as an effort to increase social distancing between passengers.
Domestic passengers are only permitted to fly without a face covering if they have a valid medical reason. This involves filling in a "Clearance-To-Fly" exemption when they arrive at the airport.
The airline's website advises those seeking exemption to arrive early, warning travellers that the screening "can take over one hour".
Delta Airlines says the process has been devised with help from the University of Pittsburgh and includes a video consultation with a doctor.
The airline warns passengers objecting to the mandatory face masks that "any false claims of a disability or health condition to obtain an exemption from wearing a mask or face covering may result in the suspension of travel privileges on any Delta flight".
According to the airline it has added 100 travellers to their no-fly list for refusing to wear a mask.
While airlines in the US including Delta have toughened up their stance on passengers refusing to wear masks, it seems passengers are now policing themselves.
Last month a confrontation was recorded on an American Airlines flight after a passenger refused to put on a mask.
On the July 19 flight from Ohio to North Carolina, a woman was berated by fellow passengers when she would not wear a face covering.
"Just leave. We have flights to get on," one passenger can be heard saying.
The woman, dubbed "Karen" by the video's recorder, is me with rapturous applause when she finally leaves the cabin and the plane is allowed to depart.