That is leaving the company vulnerable as it tries to keep its staff safe while keeping them on payrolls.
Boeing executives did not anticipate such "widespread reluctance" news wire service Reuters reported Tuesday, citing people familiar with the matter. Now the company is looking for ways to hold off "an exodus of engineering and factory labor," the Reuters report added.
Shares of Boeing closed 0.9% lower at $220.79 on Tuesday.
A federal rule mandating Covid-19 vaccinations or at least weekly testing for workers at U.S. companies with 100 or more employees has been put in place from Jan. 4.
The new guidance will cover 84 million workers, who will be required to be fully vaccinated or undergo weekly testing.
Separately, on Monday, a U.S. Judge in Fort Worth, Texas ruled in favor of air carrier United Airlines (UAL) - Get United Airlines Holdings, Inc. Report imposing a Covid-19 vaccine mandate on its employees. That mandate only provides unpaid leave to workers exempted for medical or religious grounds.
Six employees filed a suit to block the United policy in September, calling it inconsistent and in violation of the terms set by the company.
United allegedly did not accommodate exempted workers by "allowing them to continue in their role while submitting to regular testing and wearing a mask," Reuters noted in a separate report.
In his ruling Monday, District Judge Mark Pittman said “it is not for the Court to decide if United’s vaccine mandate is bad policy. Rather, it is the Court’s role to determine if Plaintiffs carried their burden to obtain a preliminary injunction.”
United said in a statement it will find "non-customer facing" roles to accommodate exempted employees, adding that those who do not apply for such positions will be put on leave.
United Airlines was the first major air carrier to impose a vaccine requirement and others have since followed. More than 96% of its workforce of 67,000 people in the U.S. is vaccinated.