(This May 16 story was refiled without any changes to text.)

By David Shepardson

WASHINGTON (Reuters) - The U.S. Department of Justice dropped a lawsuit late on Friday against Southwest Airlines ( LUV ), filed by the Biden administration in its final days, that accused the carrier of illegally operating chronically delayed flights.

The Department of Transportation filed suit in January, saying Southwest ( LUV ) operated unrealistic schedules and seeking maximum civil penalties.

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.

Southwest ( LUV ) on Friday praised the USDOT decision to abandon its lawsuit.

"The two flights at issue occurred years ago when the industry faced unprecedented challenges from the COVID-19 pandemic and were delayed due to issues outside of Southwest's ( LUV ) control in numerous cases," Southwest ( LUV ) said.

USDOT did not immediately comment Friday.

The department in January under Biden 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 earlier 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.

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

JetBlue ( JBLU ) 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.