Saying “enough is enough," thousands of workers at three Boeing manufacturing plants went on strike overnight.

Union members who assemble Boeing's fighter jets in the St. Louis area rejected the U.S. planemaker's latest contract offer on Sunday and will strike at midnight on Monday, the International Association of Machinists and Aerospace Workers union (IAM) said.

Boeing ( NYSE: BA) is confronting a fresh labor disruption as about 3,200 unionized workers at its defense facilities in the St. Louis region walked off the job after rejecting the company's latest contract offer. The strike began at midnight following a Sunday vote by members of the International Association of Machinists and Aerospace Workers.