DOT rule would require airlines to issue refunds for domestic flights delayed by 3 hours

Travelers could soon have more rights if their flight is canceled or delayed, as the Department of Transportation looks to "strengthen" protections for consumers seeking refunds.

The agency proposed a rule Wednesday that, if enacted, would define the terms of a "significant" change and cancellation for the first time.

Currently, passengers are entitled to refunds if an airline has "made a significant schedule change and/or significantly delays a flight and the consumer chooses not to travel" -- though the DOT has not yet defined what "significant" means.

Under the rule, the department would outline significant changes as:

• Changes that affect the departure and/or arrival times by three hours or more for a domestic flight or six hours or more for an international flight
• Changes to the departure or arrival airport
• Changes that increase the number of connections in the itinerary; and
• Changes to the type of aircraft flown if it causes a significant downgrade in the air travel experience or amenities a­­vailable onboard the flight.

The move comes amid increased complaints against airlines -- the majority of which concern refunds and flight service, according to data from the agency.

"I think the DOT has heard that passengers are fed up with some of the sleight of hand that airlines are pulling and some of the actions that are not consumer-friendly," Henry Harteveldt, travel industry analyst at Atmosphere Research Group, said in an interview with ABC News.

In addition, the rule would "codify the department's longstanding interpretation that a failure to provide refunds when a carrier cancels or significantly changes a flight to, from or within the United States is an unfair practice," the DOT said.

"The problem, I think, up until now has been that you as an individual traveler don't necessarily know what is a significant delay on Delta, versus American, versus Southwest, versus Spirit is -- It could be significantly different on each airline," Scott Keyes, founder of Scott's Cheap Flights, told ABC News. "And those airlines don't even necessarily mention explicitly what they consider to be a significant delay."

Since the onset of the COVID-19 pandemic, U.S. airlines have issued $21 billion in cash refunds, according to Airlines for America (A4A), the group that lobbies on behalf of all major U.S. airlines. Cash refunds accounted for 8% of passenger revenues in 2021 and 22.3% of passenger revenues in 2020, versus 4.3% in 2019, A4A said.

The public will have 90 days to comment on the proposed rule. Once that period ends, the DOT will review and analyze the comments, and then decide whether to proceed with a final rule as proposed or with modifications, issue a new or modified proposal, or withdraw the proposal altogether.

ABC News' Sam Sweeney contributed to this report.