Boeing Co could face a strike by one-third of its engineering workforce if they reject a labor contract Monday.
The vote on the four-year deal will either settle a lengthy contract dispute or potentially lead to a strike that could cripple jetliner production.
Ballots from the 7,500 technical engineers are due to be counted in Seattle Monday evening, with results expected around 10 pm Pacific Time (01:00 a.m. EDT).
The bargaining unit of technical engineers narrowly rejected the contract last month and authorized union leaders to call a strike.
The group is one of two Boeing engineering bargaining units represented by the Society of Professional Engineering Employees in Aerospace (SPEEA). The other unit, representing 15,500 professional engineers, narrowly accepted Boeing's offer.
Both units had authorized the union to call a strike in the earlier vote, but the professional engineers' authorization was moot, since they agreed to the contract and that agreement prohibits workers from striking while a contract is in effect.
Technical workers are widely expected to follow the rest of the union in approving the contract. The deal provides 5 percent annual pay raises, up from 3.5 percent in Boeing's original offer. But it would eliminate a pension for new hires, leaving them with only a 401(k) plan.
Technical workers earn less than engineers, about $79,000 a year on average, versus $110,000. Some may have voted against the offer because lower salaries gave them greater concerns about their retirement savings, SPEEA President Tom McCarty said after the earlier vote.
A strike by technical workers could slow or even halt production of all Boeing airplanes and would complicate a wide-ranging review of the 787 Dreamliner by the Federal Aviation Administration. It also could impede an investigation by the National Transportation Safety Board into charred batteries on two 787s that prompted a grounding of the entire 787 fleet last week.
When the two sides last met for talks in February, the union did not pursue the pension issue, and Boeing offered no further contract concessions.
(Reporting by Alwyn Scott; editing by Andrew Hay)