Traveling this summer? Don’t forget your mask.

The Transportation Security Administration on Friday extended a federal requirement that travelers on buses, trains, commercial flights and at airports wear face masks. The requirement was set to expire on May 11 and will now be in effect through Sept. 13.

The agency started requiring people wear masks during flights, on buses, trains and public transportation in February following an order from the Centers for Disease Control and Prevention.

Airlines have required passengers wear masks for much of the past year as Covid-19 continued to spread. Carriers have banned more than 2,000 passengers for failing to follow mask requirements.

The Federal Aviation Administration in January unveiled a “zero tolerance” policy for unruly travelers after a spike in reports, many of them from travelers who refused to wear masks.

“Mask compliance is key to confidence in air travel as we climb towards recovery, which includes international travel,” said Sara Nelson, international president of the Association of Flight Attendants-CWA, the labor union that represents cabin crews at United, Spirit and more than a dozen airlines.

“We also have a responsibility to make sure aviation isn’t contributing to the spread of the virus or any variants. We applaud Administrator Pekoske and the Biden Administration for taking action that ensures we can build back better,” Nelson said.

About half of U.S. adults are at least partially vaccinated, according to federal data. Airline executives have reported higher bookings since vaccines have rolled out and more tourist attractions reopen.