Several thousand Boeing union workers at three St. Louis-area plants who build fighter jets are planning to go on strike after rejecting a proposed contract.

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.

Described by Boeing as its "last, best and final offer", the proposal includes wage increases beyond those offered in the deal previously rejected by union members.