American Crystal Sugar union workers rejected the company's original contract for the fourth time Saturday, Valley News Live reported.
Accepting the contract, which was originally offered in July 2011, required only a simple majority. It was rejected in its closest vote so far, with a 55 percent majority.
Union employees have been locked out for 17 months while attempting to secure a new contract, the Huffington Post reported.
The union originally boasted 1300 members, but that number has since dropped by about 500.
Workers were forced off the job by management a year and a half ago after refusing to agree to the proposed contract.
Many union members have seen their unemployment insurance run out, putting an increased strain on the lockout.
Union president John Riskey said the following in a statement: "By now it should be clear that Dave Berg & Crystal Sugar's management team has no interest in ending a fiscally irresponsible lockout that has been disastrous to farmer shareholders, put the federal sugar program in jeopardy, and hurt countless families in the Red River Valley."