DALLAS (AP) — Southwest Airlines warned nearly 7,000 workers on Thursday that they could lose their jobs unless labor unions accept concessions to help the airline cope with a sharp drop in travel caused by the pandemic.

Southwest is operating far fewer flights, and it asked unions in October for help with "overstaffing costs" that it estimates will amount to more than $1 billion in 2021. Southwest asked for pay cuts of around 10% in exchange for no furloughs through next year.

The airline's top labor-relations official, Russell McCrady, said Southwest's goal is to save every job. "However, due to a lack of meaningful progress in negotiations, we had to proceed with issuing notifications," he said. The advisories to employees, known as WARN notices, are legally required 60 days before large-scale layoffs or furloughs.

McCrady said the airline is willing to resume negotiations with unions.

The warnings went to 6,828 employees including more than 2,500 ground workers and 1,500 flight attendants represented by the Transport Workers Union and 1,221 pilots, who have their own union. As of the end of September, Southwest had about 58,000 employees, including 11,000 on long-term leave.

Dallas-based Southwest, the nation's fourth-biggest airline, boasts that it has never furloughed workers in its history dating back more than 50 years. It encouraged thousands of workers to take buyouts or early retirement this year but avoided layoffs. Rivals American Airlines and United Airlines furloughed 32,000 workers between them in October.

Jon Weaks, president of the pilots' union, called the furlough notices "a sad milestone" in Southwest history.

"While this development is not completely surprising, it is incredibly disappointing to our pilots and their families who are now dealing with the stress that arrives along with this notice," Weaks said in a video to his members.

The unions said they have proposed cost-cutting measures to Southwest, but management has rejected them and refused to offer another round of voluntary buyouts.

"Sending WARN Act notices either as a scare tactic or as an actual intent to furlough when other options available were not explored is about as sad as it gets," said Lyn Montgomery, president of the flight attendants' union.

Southwest received $3.2 billion in federal aid this spring as its share of the $25 billion allotted by Congress to help airlines cover their labor costs through September. Airlines are lobbying for more taxpayer help. A bipartisan proposal unveiled in Congress this week would give them another $17 billion.

Passenger traffic on U.S. airlines is down about 60% from a year ago and is not expected to improve dramatically until a large percentage of Americans have been vaccinated against COVID-19.

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David Koenig can be reached at www.twitter.com/airlinewriter