Boeing on Tuesday sent a letter to the homes of Machinists getting ready to vote on the company's contract offer set for Friday.
The company says a yes vote will land composite wing work in Puget Sound and that Machinists will perform that work.
Some union leaders have raised questions about contract language not being enough of a guarantee. Boeing says mechanics who now build aluminum wings will be trained to build the composite wings. The company also says it's committed to assembly the 777X in Washington, along with construction of other major components such as interiors.
On the important pension issue, Boeing says the law will not allow money already invested in Machinists pensions to be mixed with the pensions covering executives.