The International Association of Machinists and Aerospace Workers said early on Saturday that it plans to hold a ratification vote on Wednesday.
The union said the Boeing offer would increase pay by 35 per cent over four years, up from 30 per cent that the company offered last month.
It also boosts the ratification bonus to $US7,000 ($A10,440) per worker instead of $US6,000 ($A8,949).
The new offer would not restore a traditional pension plan — a key demand of the 33,000 striking workers — but it would increase the amount of contributions to retirement plans that Boeing would match.
It would also retain performance bonuses that Boeing wanted to eliminate and make them at least four per cent of pay, the union said.
"The fact the company has put forward an improved proposal is a testament to the resolve and dedication of the frontline workers who've been on strike — and to the strong support they have received from so many," union district presidents Jon Holden and Brandon Bryant said in a statement.
"We look forward to our employees voting on the negotiated proposal," Boeing said.
We're fighting to save — Machinists Union (@MachinistsUnion) @Boeing.We're fighting for the flying public.We're fighting for every working family.Check out some highlights from our HUGE rally in Seattle for @IAM751 and W24 members! pic.twitter.com/7RdmMsA0a9October 16, 2024
The union credited acting Labour Secretary Julie Su for helping produce the new proposal. Su met with company and union officials this week in Seattle in an indication of the Biden administration's concern about the strike's impact on the economy.
The union said some details — including when workers would return to their jobs if they approve the deal — will be part of Wednesday's vote.
About 33,000 members of IAM District 751 began a strike on Sept. 13 after more than 94 per cent voted to reject a Boeing offer that was supported by union leadership even though it fell short of the union's goal of a 40 per cent pay raise.
Chastened union leaders declined even to call a membership vote on a Boeing offer in early October.
On Saturday, union officials stopped short of endorsing the new offer, but told members it is "worthy of your consideration".
They said that when the annual pay raises are compounded, they total 39.8 per cent.
Boeing has said that average annual pay for machinists is currently $US75,608 ($A112,764).
The strike by workers in Washington state, Oregon and California has halted production of Boeing 737s including the 737 Max, and 767s and 777s. Boeing is continuing to build 787 Dreamliners at a nonunion plant in South Carolina.
The strike has led new Boeing CEO Kelly Ortberg to announce about 17,000 layoffs and take early steps toward raising up to $US25 billion ($A37 billion) from new stock or debt to bolster the company's finances.
Boeing suppliers are feeling the pinch, too.
Spirit AeroSystems, which builds fuselages and other components for Boeing planes, said Friday that it will put 700 workers on three-week furloughs beginning later this month and will resort to layoffs if the Boeing strike continues past November.
