Airlines have a legal obligation to ensure that their flight schedules provide travelers with realistic departure and arrival times," Transportation Secretary Pete Buttigieg said in a statement.

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

Southwest Airlines was sued in federal court by the Department of Transportation, while Frontier was hit with a $650,000 fine.

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

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.

Having assessed a first-of-its-kind fine for “chronic flight delays” against JetBlue Airways, federal regulators have now moved to penalize both Southwest Airlines and Frontier Airlines for similar infractions.

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 said the U.S. District Court lawsuit it filed in California on Wednesday alleges ... The department fined Frontier Airlines $650,000 in civil penalties, with $325,000 to be paid to ...

The agency said the U.S. District Court lawsuit it filed in California on Wednesday alleges ... The department fined Frontier Airlines $650,000 in civil penalties with $325,000 to be paid to ...

US Government Sues Southwest Airlines and Fines Frontier for Chronically Delayed ... The agency said the U.S. District Court lawsuit it filed in California on Wednesday alleges that Southwest ...

From Paris to Mexico City to Hawaii and beyond, here are all the new flights coming to Phoenix Sky Harbor and Mesa Gateway airports this year.

We are just a few steps from the finish line. We want to turn what are now one- and two-hour trips into five-minute trips.”