The International Association of Machinists and Aerospace Workers (IAM) said Saturday an overnight bargaining session had led to the new Boeing offer. The union represents about 2,500 employees at the three plants.

Under the new contract offer, employees can opt to receive an $8,000 lump sum payment — minus tax withholdings — upon ratification or can choose to have the entire amount deposited in a 401(k) plan. The company is dropping its revised 401(k) match proposal.

The union local said in a web posting that if the contract is rejected, a strike would begin just at 12:01 a.m. Thursday.

Boeing said in a statement Saturday its "new offer builds on our previous strong, highly competitive one and directly addresses the issues raised by our employees. We are hopeful they will vote yes on Wednesday."

Workers at the three plants in Missouri and Illinois build the F-15, F-18, T-7A trainer, and the MQ-25 unmanned refueler. Boeing said on July 24 it was activating a contingency plan in the event of a strike.

The standoff began after the union had criticized Boeing's proposed 401(k) payments in the contract offer and workers rejected it.

"Boeing previously took away a pension from our members, and now the company is unwilling to adequately compensate our members' 401(k) plan," IAM said on July 24.