WASHINGTON (Reuters) - The Biden administration on Wednesday sued Southwest Airlines, accusing the carrier of illegally operating multiple chronically delayed flights and disrupting passengers' travel.

The U.S. Transportation Department said in its civil suit filed with the Justice Department that the carrier had operated unrealistic schedules, and said it is seeking maximum civil penalties. 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 $650,000 for operating multiple chronically delayed flights.