Boeing building next-gen 777 in Puget Sound? Not so fast.

Days after announcing its intention to build its next major jetliner in the Seattle area, aerospace giant Boeing Co. said the decision is not yet final.

At issue is a tentative labor agreement with International Assn. of Machinists and Aerospace Workers union in Washington. A vote is scheduled for Wednesday, but late Thursday the Seattle Times reported that a union leader publicly tore up a copy of the contract and announced his intention to have it withdrawn.

There’s also hesitancy among Washington state lawmakers to approve a package of bills that includes more than $8 billion in tax savings for Boeing to build the next-generation version of the 777 wide-body jet in Puget Sound.

“We chose to engage in Puget Sound first, but without full acceptance by the union and Legislature, we will be left with no choice but to open up the process competitively and pursue other options for locating 777X work,” the company said in a statement. “If this is not ratified per the scheduled union vote on November 13th, we will begin taking the next steps. “

Boeing said all of the options are “still on the table.”

Over the last several weeks, rumors have swirled about where thousands of workers would build the plane, dubbed 777X, and its massive carbon fiber wing for the next several decades. Boeing had largely been silent on where the assembly line would go.

Other rumored destinations for manufacturing the twin-aisle jet were Charleston, S.C., where Boeing builds the 787 Dreamliner; and Long Beach, where it builds the C-17 cargo jet.

The company’s Long Beach plant, which is now set for closure in 2015, had been rumored as a long-shot site for the work.

But Boeing was said to have also considered manufacturing the jet in Charleston -- the company’s first nonunion final-assembly plant. The location was selected in 2009 — one year after a strike stopped work in Washington for two months.

The 777 is one of Boeing’s best-selling models. Previous versions of the plane have been built in Washington since the early 1990s.

The machinists union said the upcoming 777X program would provide “an unprecedented degree of labor stability in the volatile and competitive industry.”

On Tuesday, Boeing and the union announced that they had struck a tentative eight-year agreement, which would take them into 2024. The union said members would lose pension plan and healthcare benefits, but the promise of the 777X could mean as many as 10,000 direct and an estimated 10,000 indirect jobs in the Puget Sound region.

“Only a project as significant as the 777X and the jobs it will bring to this region warrants consideration of the terms contained in Boeing’s proposal,” Tom Wroblewski, the union’s directing business representative, said at the time. “Not all will agree with the proposal’s merits, but we believe this is a debate and a decision that ultimately belongs to the members themselves.”

The union represents more than 35,000 Boeing workers.

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