Good news for airline travelers: the Department of Transportation on Wednesday announced it is rolling out new rules that will require airlines to automatically give cash refunds to passengers for canceled and significantly delayed flights.

"This is a big day for America's flying public," said Transportation Secretary Pete Buttigieg at a Wednesday morning news conference. Buttigieg said the new rules -- which require prompt refunds -- are the biggest expansion of passenger rights in the department's history.

Airlines can no longer decide how long a delay must be before a refund is issued. Under the new DOT rules, the delays covered would be more than three hours for domestic flights and more than six hours for international flights, the agency said.

This includes tickets purchased directly from airlines, travel agents and third-party sites such as Expedia and Travelocity.

The DOT rules lay out that passengers will be "entitled to a refund if their flight is canceled or significantly changed, and they do not accept alternative transportation or travel credits offered."

DOT will also require airlines to give cash refunds if your bags are lost and not delivered within 12 hours.

The refunds must be issued within seven days, according to the new DOT rules, and must be in cash unless the passenger chooses another form of compensation. Airlines can no longer issue refunds in forms of vouchers or credits when consumers are entitled to receive cash.

Airlines will have six months to comply with the new rules.

"Passengers deserve to get their money back when an airline owes them -- without headaches or haggling," Buttigieg said in a statement.

The DOT said it is also working on rules related to family seating fees, enhancing rights for wheelchair-traveling passengers for safe and dignified travel and mandating compensation and amenities if flights are delayed or canceled by airlines.

Buttigieg said the DOT is also protecting airline passengers from being surprised by hidden fees -- a move he estimates will have Americans billions of dollars every year.

The DOT rules include that passengers will receive refunds for extra services paid for and not provided, such as Wi-Fi, seat selection or inflight entertainment.

The rules come after the agency handed Southwest Airlines a record $140 million fine for its operational meltdown during the 2022 holiday travel season.

Buttigieg said Southwest's fine sets a "new standard" for airlines and passenger rights.

"To be clear, we want the airline sector to thrive. It is why we put so much into helping them survive the pandemic and honestly it's why we're being so rigorous on passenger protection," he said.

Buttigieg reiterated that refund requirements are already the standard for airlines, but the new DOT rules hold the airlines to account and makes sure passengers get the "refunds that are owed to them."

"Airlines are not enthusiastic about us holding them to a higher standard," Buttigieg said, adding that he "knows they will be able to adapt to this."

Airlines for America, the trade association for the country's leading passenger and cargo airlines, told ABC News in a statement that its members "offer a range of options -- including fully refundable fares." Is said consumers are "given the choice of refundable ticket options with terms and conditions that best fit their needs at first search results."

The group said the 11 largest U.S. airlines issued $43 billion in customer refunds from 2020 through 2023 nearly $11 billion in refunds just last year.