Boeing Co. expects more than 3,200 union workers at three St. Louis-area plants that produce U.S. fighter jets to strike after they rejected a proposed contract Sunday that included a 20% wage increase over four years.

ST. LOUIS — Members of the union that represents machinists at Boeing St. Louis voted on Sunday to reject the company’s offer on a new contract that included a 20% wage increase over four years.

Boeing Co. faces the risk of a strike at its St. Louis defense hub after union workers rejected a contract offer that would boost their wages by 20% over four years.