Striking Boeing workers will vote on Monday on an improved contract offer that includes a 38% pay rise over four years, a larger signing bonus and carries the endorsement of their union, which told members it had extracted all it could from the planemaker.

The latest offer, presented on Thursday, comes at a critical moment for Boeing, which this week announced it would raise up to $24.3 billion to shore up its battered finances as a seven-week strike by more than 33,000 factory workers in the U.S. West Coast 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 labor. 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.