Employees have until Dec. 8 to either "show proof of vaccination or have an approved reasonable accommodation based on a disability or sincerely held religious belief," Boeing told FOX Business in a statement.
The aerospace company said the mandate is in place to ensure that they are in compliance with President Biden's executive order for federal contractors.
Last month, Biden ordered sweeping new federal vaccine requirements for as many as 100 million Americans — private-sector employees as well as health care workers and federal contractors — in an all-out effort to curb the surging COVID-19 delta variant.
As part of the expansive rules, Biden is requiring vaccination for employees of the executive branch and contractors who do business with the federal government — with no option to test out. That covers several million more workers.
If any employees refuse to comply with Boeing's order, they "may be released from the company," the Seattle Times reports, citing an internal Boeing presentation.
Meanwhile, if an employee is granted an exemption, they will have to be tested frequently for the virus and be ready to "present a negative test result upon request."
The white-collar union the Society of Professional Engineering Employees in Aerospace says it is communicating with Boeing "to ensure implementation gives proper consideration to members’ concerns."
Boeing said it plans to continue to monitor guidance from public health agencies, and requirements from federal, state and local governments and will "prioritize the health and safety of all of our employees."
The policy will apply to roughly 140,000 employees.
The Associated Press contributed to this report.