Southwest is one of the major U.S. carriers contemplating cost cuts this summer within a travel industry that has been crippled by the coronavirus pandemic.
“Overall, I’m very pleased with the response to these programs. I’m incredibly grateful to those of you who answered the call," Chief Executive Gary Kelly said in the memo, which was first reported on by the Dallas Morning News.
"I know there are stories behind every one of those 16,895 decisions — from your incredible history at Southwest Airlines, to stories of what’s ahead in your next phase."
Southwest said it would accept applications from 4,400 workers for early retirement and evaluate nearly 12,500 requests for extended-time-off packages.
Southwest shares dropped 3% to $33.12 at last check.
Airline executives across the industry have been pushing employees to take unpaid or partly paid time off in recent weeks while also appealing for bailout funds from the federal government.
Separately, Sunday was Delta Air Lines' DAL deadline for pilots to apply for early retirement, and some 2,235 pilots signed up, according to the workers' union.
Delta previously said that about 2,600 pilots would be warned of potential furloughs once the terms of its federal financial aid expire in the fall.
Delta shares at last check fell 2.9% to $26.27.
The airline industry received $25 billion in government bailout funds during the first round of stimulus, but airlines have since said they would need more as travel restrictions to Europe and worries about coronavirus spreading domestically have hampered the industry.