United told reporters Tuesday United Airlines is planning to lay off around 600 of its employees, or about 1% of its total workforce, for failing to comply with its COVID-19 vaccine mandate. The company said Tuesday that it is already preparing to lay off the non-compliant workers.

The airline previously set a Sept. 27 deadline for all employees to provide proof of vaccination. Now that the deadline has passed, the company said it will now move to fire employees that failed to present any proof of vaccination and those that have not applied for an exemption to the rule. United said employees set to be fired will be given one more chance to comply with its COVID-19 vaccine mandate during the separation process.

United Airlines CEO Scott Kirby and President Brett Hart said in a memo to employees on Tuesday that it was a difficult decision for the company to fire non-compliant employees. The two added that the decision had to be made to ensure the safety of all workers in the company.

Less than 3% of employees at the airline had submitted a request for exemption due to religious or medical reasons. Six of those employees had filed a lawsuit against the airline after it decided to put exempt employees on unpaid leave as part of its safety protocol.

United said Tuesday that reception of its COVID-19 vaccine mandate for employees has been mostly positive and it has actually seen an uptick in applicants. The airline said its policies have attracted people who want to work in a safe environment.

"Our rationale for requiring the vaccine for all United's U.S.-based employees was simple - to keep our people safe - and the truth is this: everyone is safer when everyone is vaccinated, and vaccine requirements work," the airline said the memo.  

United is the first of the country's top four major airlines to lay off employees who refused to comply with its vaccine mandate. Other airlines have yet to implement such a drastic measure.

Instead of being fired, employees at Delta who refused to comply with its mandate were slapped with a $200 monthly fine. Meanwhile, American Airlines and Southwest Airlines have not implemented vaccine mandates and are mostly only encouraging workers to get their shots.