The strike started at Boeing facilities in St. Louis; St. Charles, Missouri; and Mascoutah, Illinois, 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, the union said.

The strike involves roughly 3,200 workers at three Boeing sites, including its St. Louis hub, which is expected to be central to the F-47 program.