Workers represented by the International Association of Machinists and Aerospace Workers at Boeing (BA  ) Defense factories in Missouri are set to go on strike after rejecting the company's contract offer.

The strike affects factories that produce a number of key defense products produced by the company. Facilities include those producing jets like the F-15 and F/A-18 in St. Louis, as well as a facility in St. Charles that creates guided munitions like missiles.

"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," IAM District 837 wrote in a statement. "Boeing previously took away a pension from our members, and now the company is unwilling to adequately compensate our members' 401(k) plan. We will not allow this company to put our members' hard-earned retirements in jeopardy."

Boeing's offer would have raised wages by 7.2% in the first year along with a $1,000 bonus, followed by raises of 4% and 3% the second and third years, respectively. The company has also said that the offer included a 10% match of base and incentive pay towards workers' 401(k) accounts.

Speaking to DefenseNews, the Chief of Staff of the IAM aerospace division, Jody Bennett, said that the union was not satisfied with Boeing's phase-out of its automatic 401(k) contributions. According to Bennett, automatic contributions have declined across the last few contracts proposed by the company, and that the union had asked the company to keep it.

Boeing has said that it is "disappointed" with the vote, calling its offer "highly competitive." The aerospace company would be activating a "contingency plan to support continuity of operations in the event of a strike."

As part of a pre-existing agreement between the two sides, the strike has been delayed until August 1 to allow a 7 day "cooldown" period. While negotiations could pick back up in that time and delay a strike, Bennett has stated that IAM and Boeing had not yet resumed talks.