ST. CHARLES, Mo. >> Roughly 2,500 Boeing workers are expected to go on strike next month at three plants in the St. Louis area after they voted Sunday to reject a contract offer from the plane maker.

The strike is planned to begin Aug. 1 at Boeing manufacturing facilities in St. Charles County, St. Louis County and Mascoutah, Illinois, after the International Association of Machinists and Aerospace Workers District 837 union voted down the contract, according to the St. Louis Post-Dispatch.

“We cannot accept a contract that is not fair and equitable, as this company continues to make billions of dollars each year off the backs of our hardworking members,” the union said.

Boing said in a statement that the Chicago-based company is disappointed in the vote, but it will now use its “contingency plan to support continuity of operations in the event of a strike.”

A Boeing spokesman said the company’s contract offer included competitive raises and a generous retirement plan that included Boeing matching employee contributions to their retirement plan up to 10% of their pay.

Boeing is expected to give an update on its finances this week when it releases its next quarterly earnings report on Wednesday. Earlier this year, Boeing reported a $1.2 billion loss in the first quarter, but just last week the company announced that Delta Air Lines had ordered 100 of its 737 airplanes.