The Centers for Disease Control and Prevention (CDC) issued a sweeping order late Friday that mandates the use of masks on airplanes and other public transportation as the U.S. seeks to contain the spread of COVID-19. "People must wear masks that cover both the mouth and nose when awaiting, boarding, traveling on, or disembarking public conveyances. People must also wear masks when entering or on the premises of a transportation hub in the United States," the CDC said in its announcement. Masks have already been required for most forms of transportation, though in many cases were required by individual companies, such as airlines. "Scientific evidence shows that consistent and universal use of masks on public transportation systems and in transportation hubs will protect Americans and help to reduce the spread of COVID-19," the agency wrote Friday in explaining why it was ordering masks now.