The International Association of Machinists & Aerospace Workers District 751 voted late Wednesday to turn down Boeing's proposal to extend by eight years the current contract that expires in 2016.
The contract extension notably would have reduced retirement benefits and provided a one percent pay raise every other year, in exchange for the long-term stability of production of the new long-range, twin-aisle plane.
A solid 67 per cent of the roughly 31,000 members of the IAM machinists union who work for Boeing in the Seattle area of Washington state rejected the deal.
"We are very disappointed in the outcome of the union vote," Ray Conner, Boeing Commercial Airplanes president and chief executive, said in a statement.
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"Our goal was two-fold: to enable the 777X and its new composite wing to be produced in Puget Sound and to create a competitive structure to ensure that we continue market-leading pay, health care and retirement benefits while preserving jobs and our industrial base here in the region," he said.
IAM representative Tom Wroblewski said the union had preserved members' pensions, "something sacred" that will help members retire with more comfort and dignity.
"It is my belief that we represent the best aerospace workforce in the world and hope that as a result of this vote Boeing will not discard our skills when looking to place the 777X," Wroblewski said in a statement.
Boeing, headquartered in Chicago, signaled that the union rejection had shut the door to further negotiations.
The spokesman declined to identify the potential 777X locations.
In late October, another Boeing spokesman, Marc Birtel, told AFP that the company would design its new 777X aircraft at five US sites and in Moscow, Russia, but had made no decision about using its key Washington state facilities.
Much of the detailed design will be carried out by Boeing engineering teams in Charleston, South Carolina; Huntsville, Alabama; Long Beach, California; Philadelphia, Pennsylvania; and St. Louis, Missouri, the company told employees in an internal memo seen by AFP.
Shares in Dow member Boeing closed 1.4 per cent higher at USD 135.09 in New York trade.