Seattle ? Machinists at Boeing Co. voted overwhelmingly Thursday to strike, rejecting a three-year contract proposal their leaders had deemed “insulting.”

The strike by more than 18,000 assembly workers at 12:01 a.m. local time today means Boeing will stop building commercial airplanes, and comes at a time when new orders had picked up in recent months. “We don’t intend to assemble airplanes during this strike,” Boeing spokesman Charles Bickers said, adding the company was “disappointed.”

Union members nationally voted 86 percent in favor of a strike.

The strike will affect Machinists who build commercial jets and some key components in the Seattle area, Gresham, Ore., and Wichita, Kan.

Employees at the Wichita plant set to walk out at 12:01 a.m. today, two hours before their colleagues in the West were to take similar action.

Steve Rooney, president of Local 70 in Wichita, said 84 percent of Machinists voted in favor of the strike.