As more passengers voice frustration with U.S. airlines over rejected refund claims amid the coronavirus pandemic, Democratic lawmakers are introducing legislation that would hold major U.S. airlines legally responsible for giving customers refunds, even if their flight was not canceled.

The Department of Transportation (DOT) reported it has received more than 25,000 travel service complaints over the last two months, "many of which concern refunds." The department said that pre-pandemic it typically received around 1,500 complaints and inquiries per month.

On Tuesday, the DOT issued its second warning to airlines related to refunds, asking them "to revisit their customer service policies and ensure they are as flexible and considerate as possible to the needs of passengers who face financial hardship during this time." The DOT said airlines are required to provide a refund to travelers if their flight is canceled or significantly changed by the airline, but not if passengers individually cancel their ticket.

The Cash Refunds for Coronavirus Cancellations Act, spearheaded by Sen. Edward Markey, D-Mass., would require the airline to "promptly offer a full cash refund for cancelled tickets" if either the airline or the passenger canceled the trip.

Markey will formally introduce the legislation Wednesday along with co-sponsors Sens. Elizabeth Warren, Richard Blumenthal, Chris Murphy and Kamala Harris.

“People are desperate, people need money, people are out of work, people are worried about taking care of their families,” Sen. Markey told ABC News.

The legislation would also require airlines to issue retroactive refunds dating all the way back to March 1.

"By March 1, it was clear that we were in a pandemic,” Markey said. "The federal government has given billions of dollars to the airlines to keep them afloat, to bail them out. Well, the airline should bail out these passengers and give them back their money as well so that they can use it to take care of their families.”

Markey said he would tie refund requirements to the next stimulus bill if necessary.

"I'm going to fight until we ultimately get this money back for passengers," Markey said. "We cannot have the airlines tipping passengers upside down and shaking money out of these passengers' pockets when they need it desperately for their own families.”

If passed, the new policies would be in effect 180 days after both the COVID-19 public health emergency declaration and presidential emergency declaration expires.

Passengers have sued major U.S. airlines such as United and Southwest over rejected ticket refund claims.

In an attempt to weather the crisis, the airline industry has taken unprecedented measures such as slashing flights, cutting executive pay, offering employees unpaid leave and parking hundreds of aircraft.

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Last week Nick Calio, CEO of Airlines for America, which represents the major U.S. airlines, told lawmakers during a Senate Commerce hearing that refunds are exceeding revenues.

"You can insist that everybody gets a refund who canceled the flight themselves instead of a voucher," Calio said. "Or you can drive the companies towards bankruptcy, which would happen very quickly at the rate things are going in terms of the revenue coming in and the refunds.”