FILE - A woman walks through unclaimed bags at Southwest Airlines baggage claim at Salt Lake City International Airport on Dec. 29, 2022. Southwest Airlines will pay a $35 million fine as part of a $140 million agreement to settle a federal investigation into a debacle last December when the airline canceled thousands of flights and stranded more than 2 million travelers over the holidays. (AP Photo/Rick Bowmer, File)

WASHINGTON โ€” Southwest Airlines is still paying for its meltdown during the 2022 holidays that stranded millions of travelers โ€” and the tab is growing.

The U.S. Transportation Department has ordered Southwest to pay a $140 million civil penalty, part of a broader consent order after the airlineโ€™s operational failures a year ago.

That penalty is by far the largest the DOT has ever levied for consumer protection violations, according to a statement from the department.

โ€œThis is not just about Southwest,โ€ Transportation Secretary Pete Buttigieg said inย an interview with NPRโ€™sย Morning Edition. โ€œThis is about the entire industry, sending a signal that you should not be cutting corners โ€” because if you fail your passengers, we will hold you accountable.โ€

A major winter storm last December caused travel disruptions across the country as airlines canceled thousands of flights. But while other airlines recovered relatively quickly, Southwest fell apart. The airline ultimately canceled 16,900 flights, stranding more than 2 million passengers.

In a statement, Southwest described the agreement as โ€œa consumer-friendly settlement.โ€ The airline says it has taken steps since last yearโ€™s disruption to improve its operational resiliency and customer care.

โ€œWe have spent the past year acutely focused on efforts to enhance the Customer Experience with significant investments and initiatives that accelerate operational resiliency,โ€ said Bob Jordan, Southwest Airlines President & CEO in a statement. โ€œOur commitment to Customers has been central to our success across our 52-year history and has helped us become one of the worldโ€™s most admired and trusted airlines.โ€

FILE – Canceled Southwest Airlines flights are displayed in red on the departures monitor at the Southwest terminal at the Los Angeles International Airport, Dec. 27, 2022. (AP Photo/Damian Dovarganes, File)

Under the agreement announced Monday, Dallas-based Southwest is required to establish a $90 million compensation system for future passengers affected by significant delays and cancellations, which counts as part of the $140 million penalty. The airline will also pay $35 million in cash to the U.S. Treasury, spread out over three years.

Southwest reported $193 million in profits during the third quarter of 2023.

The civil penalty comes in addition to $600 million in refunds and reimbursements that Southwest has paid to travelers who faced disruptions. In total, the airline will shell out more than $750 million for the holiday meltdown, DOT said.

โ€œWeโ€™re sending a message reminding airlines that there are very strong economic reasons to meet their requirements, in addition to it just being the right thing to do,โ€ Buttigieg told NPR. โ€œWe just gave them 140 million reasons to make sure that this never happens again.โ€

The U.S. airline industry as a whole has improved its operational performance since last year, Buttigieg said. The Sunday after Thanksgiving saw 2.9 million passengers fly in a single day โ€” the most ever โ€” while less than 0.5% of flights were canceled.

Flight cancellations were down significantly in the first nine months of 2023, according to data released by the DOT. But delays and mishandled luggage are still problems, consumer advocates say, as travelers remain deeply dissatisfied.

Complaints about U.S. airlines climbed sharply in the first half of the year, according to a report published last week.

โ€œBasically, the airlines are on a reputation restoration tour, because they know how bad things have been the last few years,โ€ said Teresa Murray, a consumer advocate with the U.S. Public Interest Research Group, which published the report.

Travelers filed more than 26,000 formal complaints about U.S. airlines in the first five months of 2023 โ€” more than double the number filed during the same period last year, according to the report, and on pace to break the annual record set in 2022.

โ€œLast yearโ€™s disaster ruined holiday celebrations for millions of families, many who spent Christmas weekend sleeping on the floor of airport terminals,โ€ Murray said in a statement. โ€œWe hope this penalty sends a strong message to all of the airlines that they canโ€™t play with peopleโ€™s lives like this. Travelers arenโ€™t just seat numbers. Christmas 2022 is a holiday that millions will never forget, for all of the wrong reasons.โ€