Striking Boeing workers will vote on Monday on an improved contract offer that includes a 38 percent pay rise over four years and a larger signing bonus, and carries the endorsement of their union.

The latest offer, presented on Thursday, comes after Boeing this week announced it would raise up to US$24.3 billion to shore up its battered finances as a seven-week strike by more than 33,000 factory workers in Seattle worsens its cash burn.

"In every negotiation and strike, there is a point where we have extracted everything that we can in bargaining and by withholding our labour. We are at that point now and risk a regressive or lesser offer in the future," the International Association of Machinists and Aerospace Workers (IAM) said.

In a statement, Boeing said it encourages "all of our employees to learn more about the improved offer and vote on Monday, November 4,” noting that the average machinist will make US$119,309 by the end of the contract if the offer is accepted, up from US$75,608.

This was the fourth offer made by Boeing since early September, but the third on which members have been asked to vote.

Boeing's first offer of a 25 percent wage increase, which was endorsed by the union, was rejected by nearly 95 percent of workers in September.

Last week, some 64 percent of workers rejected an offer of a 35 percent general wage increase over four years that was not endorsed by the union.

Boeing's latest offer also includes a US$12,000 ratification bonus, the IAM said in a statement. It combines a previously offered US$7,000 ratification bonus and a US$5,000 lump sum into the members' 401(k) retirement account.

The other conditions in the contract remain unchanged, such as an annual bonus and the company's commitment to build its next plane -- expected in 2025 -- in the Seattle area, where Boeing was founded in July 1916.

The negotiating team, however, had been pushing for a 40 percent wage increase, as well as the return of a defined-benefit pension that members lost a decade ago.

The strike has halted production of its strongest-selling 737 MAX jet and its 767 and 777 widebodies. (Reuters/AFP)