WASHINGTON (REUTERS) - Two senators on Monday (May 31) criticised seven major United States airlines for failing to make all pandemic-related flight credits valid indefinitely and vowed to pursue legislative or regulatory actions in response.

Democrats Edward Markey and Richard Blumenthal said the airlines trade group had "refused to offer any commitment to expand cash refund policies or eliminate expiration dates for pandemic-related flight credits".

The lawmakers said the airlines "continue to sit on more than US$10 billion (S$13 billion) in unused flight credits and are still refusing to return consumers' hard-earned money, more than a year after the pandemic began".

Without removing expiration dates, "your company may be encouraging travellers to fly before they feel safe boarding a plane, lest they lose tickets that they have already purchased", they added.

On Friday, trade group Airlines for America representing American Airlines, United Airlines, Delta Air Lines, Southwest Airlines and others told the senators in a letter that major US airlines issued US$12.84 billion in cash refunds to customers last year as the coronavirus pandemic upended the travel industry.

The group declined further comment on Monday.

Airlines have faced criticism over their handling of redemptions for flights cancelled during the pandemic.

In the letter, Mr Nicholas Calio, the group's chief executive, said US airlines had maintained a steadfast commitment to the travelling public during the pandemic and issued refunds in accordance with all federal laws and regulations.

The cash refunds, which accounted for about 20 per cent of airline revenues last year, came on top of billions of dollars of travel credits that are now being used "at a rapid clip" to book fresh flights, he said.

The redemption of vouchers currently accounted for 10 per cent to 15 per cent of carriers' monthly ticket sales and was expected to increase in coming months as the pandemic winds down, Mr Calio added.