Members of the largest union at Boeing Co.'s (BA) commercial aircraft division in Wichita on Tuesday turned down a labor agreement that Onex Corp. (search) said was vital in its plan to buy the plant.

Members of the International Association of Machinists and Aerospace Workers (search) rejected the proposal by 57 percent, said Lodge 70 President Steve Rooney. The union declined to say how many of its 5,300 members at the plant voted Tuesday.

"The membership has spoken," Rooney said. "The next step is Onex's."

A spokesman for Onex didn't return phone calls for comment. However, the company previously had said it would walk away from the deal if the union rejected the agreement.

Union members had been critical of the proposal, which required a 10 percent pay cut and other concessions.

Members were also angry after Onex sent notices to 800 employees at the plant over the weekend, notifying them that they would not be rehired and telling them not to come into work on Monday. Union officials said they didn't know how many of those 800 workers belonged to the union.