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

Southwest Airlines Co. was sued by the US Transportation Department for allegedly violating rules that require airlines to set and meet realistic flight schedules.

The Department of Transportation on Wednesday sued Southwest Airlines, alleging the carrier operated chronically delayed flights, and fined Frontier Airlines for late-arriving flights.

The Transportation Department said in a lawsuit that two of the airline’s routes were consistently delayed in violation of federal rules.

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