The machinists’ union at Boeing has voted to authorize a strike against the company’s defense unit in St. Louis.

The current contract expires May 20th. The strike authorization becomes effective if no new contract is decided by then.

The union says the two sides are widely separated on some issues. Serious negotiations start next week. A company spokesman says Boeing expects "vigorous discussions" but eventual success. The union says seniority and health insurance issues are the biggest hang-ups.