The US Department of Transportation is flexing its muscles against airlines who operate chronically late flights.

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

The US Department of Transportation (DOT) has sued Southwest Airlines for allegedly operating numerous "chronically delayed" flights in violation of federal laws prohibiting deceptive practices.

Co. was sued by the US Transportation Department for allegedly violating rules that require airlines to set and meet realistic flight schedules. The carrier was responsible for “unlawful chronic flight delays” that disrupted passengers’ travel plans,

Transportation Department sues Southwest Airlines, seeking over $2.1 million in penalties for chronically delayed flights.

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

The U.S. Department of Transportation sued Southwest Airlines Wednesday, alleging it illegally operates flights that are persistently delayed, harming passengers and fair competition in the airline industry.

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.