(Reuters) -Unionized workers who assemble Boeing's fighter jets in the St. Louis area rejected Boeing's latest contract offer on Sunday and will strike at midnight on Monday, the International Association of Machinists and Aerospace Workers union said.

The rejected deal featured a 20% wage increase – 8% in the first year, and 4% percent each in years two through four for most union members.

The union representing about 3,200 St. Louis-area workers has rejected the company’s latest contract offer.