More than 3,200 Boeing defense workers have rejected the latest contract offer from the company and are preparing for a possible strike.

The threat of labor unrest follows last year’s two-month strike by a separate machinists union in Seattle, which disrupted Boeing’s ( BA) commercial jet production and prompted the company to raise $24 billion through an equity offering to offset the financial toll.

ST. LOUIS — Members of the union that represents machinists at Boeing St. Louis voted on Sunday to reject the company’s offer on a new contract that included a 20% wage increase over four years.