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

The US Department of Transportation sued Southwest Airlines and fined Frontier Airlines for flight delays, seeking civil penalties against Southwest and imposing a $650,000 fine on Frontier, part of a broader crackdown on airline delay issues.

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.

(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.

United States and U.S. Department of Transportation DOT announced a lawsuit against Southwest Airlines (LUV) for illegally operating multiple

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 department filed the lawsuit in the U.S. District Court for the Northern District of California, and seeks "maximum civil penalties." The lawsuit focuses on a route between Chicago Midway and Oakland,

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

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

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

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.