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

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

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

Southwest Airlines removed a pilot from duty after he was extracted from the cockpit of a plane and arrested for DUI.

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 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.

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.

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

Plans are underway to accommodate some visitors in town for the inauguration at the city's pro basketball and hockey arena.

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.