WASHINGTON (Reuters) - The Justice Department on Tuesday said it is in talks with Southwest Airlines ( LUV ) about potentially resolving a suit filed by the Biden administration accusing the carrier of illegally operating chronically delayed flights.

The U.S. Transportation Department in January said Southwest ( LUV ) had operated unrealistic schedules, and said it was seeking maximum civil penalties.

The Justice Department said on Tuesday it is engaged in discussions with Southwest ( LUV ) "about a potential resolution of this action," and Southwest ( LUV ) now has until May 30 to respond to the lawsuit.

Southwest ( LUV ) did not immediately comment.

USDOT said in January that for five months in 2022, Southwest ( LUV ) operated two chronically delayed flights: one between Chicago Midway and Oakland, California, and another between Baltimore and Cleveland.

The department in January fined Frontier Airlines $650,000 for operating multiple chronically delayed flights. Frontier was required to pay $325,000 and will pay the remainder if it operates any chronically delayed flights in the next three years.

Southwest ( LUV ) said in January it was disappointed USDOT chose to sue "over two flights that occurred more than two years ago." Southwest ( LUV ) said that since 2009, the carrier has operated more than 20 million flights with no other violations.

Under USDOT rules, a flight is chronically delayed if it is flown at least 10 times a month and arrives more than 30 minutes late at least 50% of the time.

Southwest ( LUV ) in December 2023 agreed to provide $90 million in travel vouchers of $75 or more to passengers delayed at least three hours getting to final destinations because of an airline-caused issue or cancellation, part of a USDOT settlement over the carrier's December 2022 holiday meltdown.

USDOT in January imposed a $2 million penalty on JetBlue Airways for operating four chronically delayed flights on domestic routes. It was the first such fine on an airline for the prohibited scheduling practice.

JetBlue agreed to pay a $1 million fine and provide vouchers worth a minimum of $75 for passengers for future flight cancellations or delays of three hours or more caused by the airline within the next year.

(Reporting by David Shepardson; Editing by Chris Reese and Nick Zieminski)