LOS ANGELES — Negotiators for Boeing Co. and its largest white-collar union are due to return to the bargaining table this week after rank-and-file members rejected the company’s latest contract offer.

Members of the Society of Professional Engineering Employees in Aerospace (SPEEA) turned down by a margin of more than 95 percent Boeing’s proposed four-year contract, which covers more than 23,000 union engineers and technicians, it said.

This week’s vote didn’t authorize a strike. Instead, it was held to underline SPEEA leaders’ contention that Boeing’s proposal was a nonstarter and that its "overwhelming" rejection would "send a loud message" to Boeing management to make major changes to its offer. Earlier, the union’s bargaining unit councils unanimously turned down the offer.

While Boeing’s existing contract with the SPEEA expires Oct. 6, the earliest a strike could begin is Nov. 25, according to terms of the existing contract. A separate strike vote would have to be held prior to a walkout.

"We hope the vote results clear away the nonsense and allow us to begin substantive negotiations," SPEEA executive director Ray Goforth said.

An SPEEA spokesman in Tukwila, Wash., later said that the company’s offers had been "so atrocious that they’re not salvageable," leading union negotiators to decide to "let the members weigh in" this week.

"(In) the spirit of good faith, we will continue to listen closely to (the SPEEA) negotiations team," Chicago-based Boeing said.

Among the key areas of dispute in Boeing’s proposed package are the size of the wage hikes over the life of the contract, higher employee contributions to the medical coverage plan, a shift from a traditional pension plan to a defined-contribution 401(k) plan for new hires in 2013 and language that the union charges would allow Boeing to alter the terms of the contract even following ratification.

While there’s speculation that negotiations could continue for several months, the SPEEA spokesman said that the union is hopeful the company will bring "reasonable proposals" to the bargaining table.