Employees at Boeing’s St. Louis defense factories rejected a contract offered by the aerospace giant Sunday afternoon and around 3,200 workers began striking starting at midnight—the first walk out the company has faced at its St. Louis defense hub since 1996.

Three Boeing defense plants face a strike as 3,200 machinists walked off their jobs. Members of the International Association of Machinists voted to strike.

The strike started at three Midwest manufacturing plants after about 3,200 local members of the International Association of Machinists and Aerospace Workers voted Sunday to reject a modified four-year labor agreement,