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

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

(ABC 6 News) — The U.S. Department of Transportation says it is prepared to take airlines to court over flight delays. The agency has filed a lawsuit against Southwest, accusing the airline of illegally operating chronically delayed flights and disrupting passengers’ travel plans.

The agency is seeking civil penalties against Southwest Airlines, and also fined Frontier Airlines for its continuous delays.

Southwest is disappointed that DOT chose to file a lawsuit over two flights that occurred more than two years ago," a spokesperson for the airline said.

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

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.

A lawsuit filed against Southwest alleges the airline operated multiple “chronically delayed” flights affecting thousands of passengers.

The lawsuit filed in California alleges that Southwest illegally operated chronically delayed flights and disrupted passengers’ travel plans.

The department's investigation found two Southwest Airline flights were delayed for five consecutive months in 2022. Both delayed flights resulted in more than 90% of disruptions between April and August that year.