The International Association of Machinists District 751 announced Wednesday night that the proposal was rejected by 67 percent of its members.
Union members who called for a no vote did so to protest the Boeing Co.'s push to end a traditional pension plan and increase their health care costs. Workers would have received a $10,000 signing bonus if they approved the deal.
"We preserved something sacred by rejecting the Boeing proposal. We've held on to our pensions and that's big. At a time when financial planners are talking about a 'retirement crisis' in America, we have preserved a tool that will help our members retire with more comfort and dignity," said Tom Wroblewski, District 751 president in a statement.
Boeing had proposed the eight-year contract extension, saying it needs the deal to assemble the new 777X in Washington state. With the threat of those jobs going to another state, lawmakers rushed to approve $8.7 billion in tax breaks last week.