Management told employees Thursday that after-market engineering work on modifying jets for current customers and converting aging passenger jets to freighters will move from Bellevue and Everett to Long Beach, Calif.
About 375 engineers now do that work near Seattle.
Boeing spokesman Jim Condelles said it's not yet clear how many of them will be affected.
"Some jobs will go away," said Condelles. "It's not to say all those jobs will move."
Boeing engineering chief Mike Delaney in May announced the company would establish new engineering centers in southern California and South Carolina.
Delaney announced at that time that a separate set of engineering work -- modifying out-of-production airplanes such as older 737s and 757s -- would move from Tukwila to Long Beach, affecting as many as 300 jobs.
Condelles said the new move involves a separate group of engineers who work on modifications such as aircraft performance upgrades or interior re-finishing as well as passenger jet-to-freighter conversions.
Delaney, in his May message, said that "we expect the Southern California and South Carolina design centers to grow over time" and that "we are presently studying other potential work packages" for those centers.
The Bellevue and Everett engineering group was the target of one of those studies.
In an internal message Thursday, Tim Copes, vice president of Fleet Services, told employees, "We have now completed that study and have decided to place the majority of the Modifications and Freighter Conversions engineering statement of work in Long Beach starting in the second half of 2013."
Copes said the engineering unit "will gradually shift its operations to Southern California over the next 18 months."
Boeing currently has about 2,000 after-market airline-support engineers in Tukwila, 500 more in Everett and 500 in Long Beach.
Copes's note said he'll hold all-employee meetings in Bellevue on Monday to discuss the company's action.