The no-fly list aboard Delta has grown to 550 people who refused to comply with their face mask policy. Delta CEO Ed Bastian sent a memo Thursday to employees, stating:

''We’ve now added a total of nearly 550 people to our no-fly list for refusing to comply with Delta’s mask requirement on board. Fortunately, that number represents a tiny fraction of our overall customers, that vast majority of whom follow our guidelines and appreciate the steps we are taking to keep them safe and healthy.''

According to The Hill, Bastian said there were 100 people on the no-fly list in July.

The Centers for Disease Control and Prevention on Tuesday updated its guidance on face masks, saying that face coverings with several layers of protection offer the most security against COVID-19 for both the general public and the mask-wearer.

Bastian also urged Delta employees to monitor their own health symptoms.

''Please continue to conduct a self-assessment every day for symptoms before coming to work and remember mask-wearing continues to be essential and required,'' he wrote in a memo, according to The Hill.

In June, Airlines for America, a trade organization which represents Delta and other major carriers in the U.S., said that customers could be put on a no-fly list if they refuse to wear face coverings. In June, United Airlines announced that it would ban passengers who refuse to wear a mask on board flights for a period of time determined by a security review.