Machinists at Boeing's St. Louis defense systems plant have authorized a strike if a contract is not accepted before the current agreement expires next month.
The International Association of Machinists and Aerospace Workers District 837 said in a statement that the strike authorization vote was supported by 99 percent of the workers who attended a meeting on Sunday.
District 837 president Gordon King says seniority, pension, health care and job protection are the key issues.
The current contract expires June 13. The union has not been on strike since Boeing purchased McDonnell Douglas. The last walkout was in 1996.
Boeing said in a statement that it expects negotiations to lead to a new contract.