The Machinists union began formal negotiations with Onex on Thursday on a labor agreement that, if approved by members, would likely take effect when the Canadian investment firm takes control of Boeing's commercial aircraft business in Wichita.
But the union noted that if members reject the investment firm's final offer, Onex could pull out of the deal.
"If the offer is accepted by the membership, Onex moves forward to complete the sale with Boeing," Machinists president and directing business representative Steve Rooney wrote in the letter to members posted on the union's Web site.
"If the membership rejects the last, best, and final offer, it is possible that Onex could choose not to pursue the purchase of the Wichita facility and it would remain Boeing for now."
Neither Rooney nor an Onex spokesman could be reached for comment Thursday evening.
Boeing spokesman Dick Ziegler said that he would not speculate on what Onex would do.
"I think it's awfully speculative to even contemplate something like that," Ziegler said. "It's a 'what-if' and we're not going to play what-if games."
The Machinists union is Boeing's largest and one of several that will need to negotiate new terms with Toronto-based Onex .
Although Thursday's meeting marked the beginning of formal negotiations, the Machinists had some insight into the terms Onex will pursue. The company gave the union its opening proposal earlier this month, according to letter.
"In that draft, we have found components that are unacceptable," Rooney wrote in the letter. "That is why the negotiation process has begun."
If members reject Onex's best and final offer, they would not strike. Everything is subject to negotiation, Rooney said in another memo posted on the Web site.
"It is vitally important that we continue to organize and grow our membership to better our bargaining position.," he said in the letter.