One of Boeing's chief labor unions staged rallies in and around Seattle this week, calling attention to a vote set for Monday that will show whether workers are willing to accept a less generous contract offered by Boeing Co or move closer to a strike.

Hundreds of engineers and technicians marched at the company's two plants, its downtown Seattle office and other facilities with signs saying "Boeing: Hands Off My Healthcare" and "We Delivered. Will Boeing?"

It was the most visible sign of rising tension over contracts covering 23,000 members of the Society of Professional Engineering Employees in Aerospace. The contracts, which affect two bargaining units, expire on October 6, and a separate vote would be needed to authorize a strike.

Though the union is widely expected to vote down the current offer, local officials and analysts consider a strike unlikely, because both sides have so much to lose and workers can keep using the current contract even after it expires.

Stan Sorscher, a Speea labor representative and former engineer, estimated the chance of a strike at 35 percent. Scott Hamilton, managing director at consulting firm Leeham Co., said Boeing likely will make a second contract offer and that will restart negotiations.

"We believe we can get to an agreement," said Doug Alder, a Boeing spokesman. "Nobody here is talking about" a strike. "Nobody wants that."

Still officials and analysts say it is worrying that Boeing's first offer is going to a vote amid worker rallies.

REASONS TO AGREE

Boeing has a backlog of 4,057 orders, and is racing to speed up its factories to make more jets, especially 787 Dreamliners, whose customers have been waiting through years of delays.

Boeing also is deciding on specifications for a new derivative of its popular 777. And it needs engineers to help repair a number of 787s that rolled off the line with flaws and must be fixed before they can be delivered. While in limbo, the jets weigh on Boeing's financial performance, analysts said.

"A strike by Speea would cripple Boeing," said Ray Goforth, Speea's executive director. "They cannot deliver airplanes without our members" who are involved in certifying jets before they go to customers.

For the union, a strike could reduce its relevance and its ranks, which already are under pressure from retirement of senior workers and outsourcing.

Boeing has moved large amounts of engineering work to its suppliers and aims to move more despite the technical problems and cost overruns that resulted from using foreign engineers for the 787. Various engineering groups did not coordinate well, and key pieces, such as wings, did not work well and needed to be re-engineered.

Boeing attributes those problems at least in part to flawed execution of the distributed engineering model, not the model itself, and says it will continue to tap engineers from anywhere, even if not from Speea's mostly Puget Sound workforce.

Goforth, the Speea leader, said the union could do damage without a strike, by having engineers "work-to-rule" - refusing overtime and following all procedures.

"Boeing has more rules, regulations and guidelines than any company I've ever seen," he said. "If the employees start strictly complying with all of them, you'd see productions problems immediately and the employees would still be collecting paychecks."

Investors and customers could lose in either scenario. Boeing's stock price, which closed at $69.60 on Friday, up 12 percent in the last year, likely would fall, and plane deliveries would be delayed.

"I hope they resolve it," Tim Clark, president of Emirates airline, Boeing's biggest 777 customer with 75 unfilled orders, said of the labor trouble while in Seattle on Thursday.

"I hope our orders and those of others help give them a way through."