Delta already has banned some passengers refusing to wear masks

Delta Air Lines has already banned some passengers who refused to wear masks, according to CEO Ed Bastian.

The Atlanta-based airline said earlier this month that those who do not comply with its requirement to wear a mask in flight "risk future flight privileges with Delta."

Bastian wrote in a memo to employees Thursday: "We take the requirement to wear a mask very seriously." Passengers "must follow crew member instruction to properly wear them in flight."

“So far, there have thankfully only been a handful of cases, but we have already banned some passengers from future travel on Delta for refusing to wear masks on board,” Bastian wrote in the memo.

Other airlines have rolled out similar policies requiring masks and threatening to ban passengers who do not comply.

Delta, the dominant airline at Hartsfield-Jackson International Airport, says on its website that customers and employees are required to wear a face mask or face covering over their nose and mouth throughout travel, including at check-in, gate areas, jet bridges and on board the plane except during meal service.

>>>RELATED: Hartsfield-Jackson faces hurdles enforcing masks

Delta’s policy also says: “People unable to keep a face covering in place, including children, are exempt, along with those who have trouble wearing a mask due to an underlying medical condition. Customers are encouraged to communicate their exception with a Delta representative when asked to wear a face covering.”

Passengers are encouraged to bring their own mask, but Delta can also provide masks to those who don’t have them.

Delta has also started testing its employees for the coronavirus and antibodies in Atlanta, in addition to its Minneapolis hub. Bastian said he has been tested several times and would be tested again Thursday.

>>>RELATED: Delta says 500 employees tested positive for COVID-19

He added that he expects travel demand this summer to be down at about a quarter of last year’s levels. The airline is ramping up flights in July and August but is “unlikely to add may more flights for the remainder of the year beyond what we have in August.”