SEATTLE – Leaders of more than 18,000 machinists are advising workers to reject Boeing’s final contract offer and strike – a scenario a top Boeing executive called devastating to the company’s prospects.

Union members are voting on the three-year offer today, with the current contract set to expire Friday. In a statement late Tuesday on its Web site, Seattle-based Machinists Lodge 751, which represents workers who assemble commercial airplanes, said the company was insisting on concessions and takeaways in a “corporate strategy to break the workers who have built this company.”

If the union members vote to strike, the head of Boeing’s commercial airplanes division, Alan Mulally, said the company would have no choice but to slowly shut down operations. And if that happens, Mr. Mulally said, customers have been clear they’d likely take their business to Boeing’s prime rival – Airbus SAS.

“I just cannot emphasize enough what a strike would mean to us because we would absolutely be walking away from our commitments to our customers,” Mr. Mulally said Tuesday. “There’s just no way we would recover.”

It’s been 10 years since the union went on strike. “No one ever wants to strike, but withholding your labor is the only way to stop this attack on American workers,” the union statement said.