The carrier explained that its contracts with the federal government makes them a government contractor, so it is covered by President Joe Biden's order directing contractors to mandate vaccines for employees.
On Friday, American Airlines, Alaska Airlines and JetBlue also announced a vaccine mandate for employees to comply with the federal order.
United Airlines took an early stance to require COVID-19 vaccination. United said Thursday that 320 of its 67,000 U.S. employees face termination for not getting vaccinated or seeking a medical or religious exemption by last week's deadline.
Southwest said its employees must be fully vaccinated against COVID-19, or get an approved exemption, by Dec. 8.
Airlines are large employers that fall under Biden's sweeping order that companies with more than 100 workers require employees to be vaccinated or undergo weekly testing for the virus.
However, they are also government contractors, who face a Dec. 8 deadline to enforce vaccination requirements — without the testing option.
“Southwest Airlines must join our industry peers in complying with the federal government's COVID-19 vaccination directive,” Gary Kelly, Southwest Airlines Chairman and CEO said in a statement. “I encourage all Southwest Employees to meet the federal directive, as quickly as possible, since we value every individual and want to ensure job security for all.”
The pilot union at American recently estimated that 4,200 — or 30% — of the airline's pilots are not vaccinated.
Delta said last week that it was still evaluating Biden's order. The airline previously said it will require vaccination or weekly testing and impose surcharges on unvaccinated employees.
The Associated Press contributed to this report.