Airlines must fully refund airfare to passengers whose flights have been canceled during the outbreak of Covid-19, the U.S. Transportation Department ordered on Friday.

The DOT is receiving growing numbers of complaints from people who say airlines have denied refunding their money after flights were canceled, the agency said in a press release.

“The obligation of airlines to provide refunds, including the ticket price and any optional fee charged for services a passenger is unable to use, does not cease when the flight disruptions are outside of the carrier’s control,” the agency said.

The policy also applies when an airline “makes a significant schedule change and the passenger chooses not to accept the alternative offered by the carrier,” DOT said.

As of Thursday, passenger traffic had fallen about 95% compared to a year ago, according to the Transportation Security Administration. Only 124,021 passed through security that day compared to 2.4 million on the equivalent day in 2019.

In response, airlines have canceled thousands of flights.