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 lawsuit follows a DOT fine on JetBlue Airways for similar allegations.

The lawsuit and fines come at the end of the Biden administration, which has taken a harder line toward consumer protections than previous administrations.

The DOT said that Southwest’s flights from Chicago Midway International Airport to Oakland, Calif. and from Baltimore to Cleveland arrived late nearly 200 times between April and August 2022.

“Each flight was chronically delayed for five straight months,” the DOT said. It said the airline was responsible for more than 90% of the disruptions.

Southwest didn’t immediately respond to a request for comment.

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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 lawsuit follows a DOT fine on JetBlue Airways for similar allegations.

The lawsuit and fines come at the end of the Biden administration, which has taken a harder line toward consumer protections than previous administrations.

The DOT said that Southwest’s flights from Chicago Midway International Airport to Oakland, Calif. and from Baltimore to Cleveland arrived late nearly 200 times between April and August 2022.

“Each flight was chronically delayed for five straight months,” the DOT said. It said the airline was responsible for more than 90% of the disruptions.

Southwest didn’t immediately respond to a request for comment.

This is breaking news. Please refresh for updates.