The Department of Transportation said Friday that airlines must give customers refunds when flights are canceled or significantly delayed amid the coronavirus.

The agency said it has received an increasing number of complaints from airline customers who said they were denied refunds for canceled or significantly delayed flights and instead given vouchers to use for travel at a later date.

Airlines have axed thousands of flights and are continuing to cancel planned flights through the summer after the virus and measures to stop it from spreading, such as stay-at-home orders, devastated travel demand.