Starting today, United Airlines requires all flight attendants to wear masks while on board aircraft.
The company is the largest U.S. carrier to adopt that policy, which has previously been put in place at Frontier Airlines.
United says the order is in keeping with social-distancing guidelines from the Centers for Disease Control and Prevention.
According to CNN, flight attendants will have the option of wearing their own face coverings or using masks provided by the company.
The Association of Flight Attendants, a union that represents workers at United and 19 other airlines, supports the measure. But as Reuters reports, the union sent a letter Thursday to the Department of Transportation and the Department of Health and Human Services imploring the federal government to require airline passengers to wear face coverings as well.
Canada now requires passengers to wear masks on flights operating within that country, but the United States has not yet issued such an order.