Boeing workers who build fighter jets went on strike Monday at midnight Central Daylight Time. About 3,200 workers at Boeing facilities in St. Louis; St. Charles, Missouri; and Mascoutah, Illinois, voted to reject a modified four-year labor agreement with Boeing, the International Association of Machinists and Aerospace Workers union said Sunday.

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.

Some 3,200 Boeing workers who build fighter jets in St. Louis and another Missouri site and one in Illinois are on strike, their union says.