SEATTLE (AP) — Aircraft assembly workers walked off the job early Friday at Boeing factories near Seattle after union members voted overwhelmingly to go on strike and reject a tentative contract that would have increased wages by 25% over four years.

The strike started at 12:01 a.m. PDT, less than three hours after the local branch of the International Association of Machinists and Aerospace Workers announced 94.6% of voting workers rejected the proposed contract and 96% approved the work stoppage, easily surpassing a two-thirds requirement.

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 airline planes. The strike will not affect commercial flights but represents another setback for the aerospace giant, whose reputation and finances have been battered by manufacturing problems and multiple federal investigations this year.

The striking machinists assemble the 737 Max, Boeing’s best-selling airliner, along with the 777, or “triple-seven” jet, and the 767 cargo plane at factories in Renton and Everett, Washington. The walkout likely will not stop production of Boeing 787 Dreamliners, which are built by nonunion workers in South Carolina.

Outside the Renton factory, people stood with signs reading, “Historic contract my ass” and “Have you seen the damn housing prices?” Car horns honked and a boom box played songs such as Twisted Sister’s “We’re Not Gonna Take It” and Taylor Swift’s “Look What You Made Me Do.”

Boeing responded to the strike announcement by saying it was “ready to get back to the table to reach a new agreement.”

“The message was clear that the tentative agreement we reached with IAM leadership was not acceptable to the members. We remain committed to resetting our relationship with our employees and the union,” the company said in a statement.