More than 3,200 union members who assemble Boeing's fighter jets in the St. Louis area and Illinois went on strike on Monday after rejecting a second contract offer the previous day. Boeing Defense said it was ready for the work stoppage and it will implement a contingency plan that uses non-labor workers.

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.

About 3,200 workers who build F-15 fighter jets and other military aircraft voted to reject the firm's latest offer.