SEATTLE, WA (AP, MyBellinghamNow.com) – Boeing aircraft assembly workers have walked off the job after union members voted overwhelmingly to reject a tentative contract that could have increased wages by 25% over four years.

The strike started less than three hours after 94.6% of voting workers rejected the proposed contract and 96% approved the work stoppage.

The labor action involves 33,000 Boeing machinists, most of them in Washington state, and is expected to shut down production of the company’s best-selling planes.

The strike will not affect commercial flights.

The union wanted to restore traditional pensions that were axed a decade ago but settled for an increase in new Boeing contributions to employee 401(k) retirement accounts.

Several workers said they considered the wage offer inadequate and were upset by a recent company decision to change the criteria on which annual bonuses are paid.

Depending on how long the strike lasts, suspension of airplane production could prove costly for the beleaguered Boeing.

Jefferies aerospace analyst Sheila Kahyaoglu estimated a strike would cost the company about $3 billion.