The lawsuit alleges Southwest illegally operated chronically delayed flights and disrupted passengers' travel plans.

The US Department of Transportation (USDOT) is suing Southwest Airlines for “illegally operating multiple chronically delayed flights and disrupting passengers’ travel,” according to a press release.

The Department of Transportation is suing Southwest Airlines, accusing it of operating two “chronically delayed flights” in 2022 that resulted in 180 flight disruptions.

The DOT is aiming to send a message to all airlines that it will go to court to enforce passenger protections.

The U.S. Transportation Department is suing Southwest Airlines and has fined Frontier Airlines over "chronically" delayed flights, disrupting passengers' travel and plans.

Southwest Airlines stock fell Thursday after the Department of Transportation sued the airline over a pair of "chronically delayed flights."

The Department of Transportation is suing the airline for what it characterized as months of "chronically delayed" flights — those that arrive at least 30 minutes late more than half the time.

The Department of Transportation said that two Southwest Airlines routes arrived late nearly 180 times in a five-month period in 2022.

This "sends a message to all airlines" that DOT will go to court in order "to enforce passenger protections," Pete Buttigieg said.

The Transportation Department is stepping up enforcement of persistent flight delays with a civil lawsuit against Southwest Airlines and a fine against Frontier Airlines.

The Transportation Department also announced $650,000 in civil penalties against Frontier Airlines on Wednesday, citing chronically delayed flights. $325,000 will be paid to the U.S. Treasury while the remainder can be suspended if Frontier does not operate more chronically delayed flights in the next three years.