Travelers on airplanes and public transportation like buses and subways will be required to wear face masks starting on Monday to curb the spread of COVID-19.

The U.S. Centers for Disease Control and Prevention (CDC) issued a mask-wearing rule late Friday that builds on an order announced January 21 by President Joe Biden. 

The rule "will protect Americans and provide confidence that we can once again travel safely even during this pandemic," said Dr. Marty Cetron, director of CDC's division of migration and quarantine, who signed the order. 

The 11-page CDC order takes effect just before midnight on Monday night. It makes refusal to wear a mask a violation of federal law, enforced by the Transportation Security Administration and other federal, state and local authorities. 

The rule applies to passengers on airplanes, trains, subways, buses, taxis and ride-shares. It says travelers must wear a mask that covers their nose and mouth while riding and while getting on and off rides. The order extends to waiting areas such as airports, train platforms and subway stations. 

Airlines already require masks and have banned more than 2,000 passengers for refusing to wear one. Flight attendant unions have said a federal rule will make it easier for crews to enforce the requirement. 

The order exempts children under 2 years of age and people with a disability that makes it unsafe to wear a mask. Airlines struggled with an exemption for safety and stopped allowing it. The CDC said transportation operators can require medical documentation. 

Travelers will be allowed to remove masks while eating or drinking. 

The CDC said some face coverings aren't good enough to comply with the rule. The don't-travel list includes face shields, bandanas, masks with exhalation valves and masks that are too big or otherwise don't fit properly. 

The CDC said transportation operators may require a negative COVID-19 test from passengers. Cetron said this week that the health agency is considering requiring testing of passengers on flights within the United States, but the airline industry is fighting a testing requirement out of fear that fewer people will fly. U.S. air travel is already down more than 60 percent from a year ago. 

The CDC rule came just over a week after Biden's executive order, which already mandated masks on certain modes of public transportation including planes and trains, and it mandated masks on federal property.