The Transportation Department is stepping up enforcement of persistent flight delays with a lawsuit against Southwest Airlines and a fine against Frontier Airlines.

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 department said Southwest operated two chronically delayed flights – one between Chicago and Oakland, California, and another between Baltimore and Cleveland for five months in 2022. The department also said on Wednesday that it was fining Frontier Airlines $650,

DOT sues Southwest Airlines, accusing the airline of chronic flight delays while citing unrealistic scheduling that disrupted passengers.