President Joe Biden on Thursday signed an executive order requiring masks to be worn on airplanes, trains, buses and at airports as coronavirus infections continue to climb.

The Trump administration declined to mandate masks in air travel and other modes of transportation, leaving it to private companies to set their own polices, though the Centers for Disease Control and Prevention has repeatedly recommended their use.

That has left flight attendants and other employees to enforce the rules and labor unions that pushed for a federal mask mandate cheered Biden’s order.

“Today’s executive action on a mask mandate for interstate travel, including airports and planes, will provide much needed back up for Flight Attendants and aviation workers on the frontlines,” Sara Nelson, president of the Association of Fight Attendants-CWA, the country’s largest flight attendant labor union, said in a statement.

All major U.S. airlines require travelers to wear masks on board — a policy that extends to airports. Airline executives say the vast majority of customers follow the rule, but they have vowed to take a hard line against those who refuse. Through last week, airlines have barred more than 2,500 people from flying for refusing to wear face coverings. The FAA noted that some rare cases have even turned violent.

The FAA this month warned it will crack down on unruly behavior and on travelers who don’t follow crew instructions.