FILE - In this April 23, 2020 file photo a Frontier Airlines jetliner taxis to a runway for take off from Denver International Airport in Denver. There are thousands of airline customers who have canceled bookings because of the coronavirus epidemic and haven't gotten their money back. Sen. Edward Markey, D-Mass., and four other Senate Democrats proposed legislation on Wednesday, May 13, 2020 that would require airlines to give full cash refunds to passengers during the pandemic, even if it was the customer who canceled. Frontier has offered only a travel credit instead of a full refund. (AP Photo/David Zalubowski)