Union workers at American Crystal Sugar, who have been locked out of their jobs for 20 months, will vote for the fifth time on essentially the same contract on April 13.

Crystal's 1,300 workers have rejected the contract four times, but by decreasing margins in what has become one of the longest work stoppages in Minnesota history. The last vote, held Dec. 1, was shot down by 55 percent of workers, down from 63 percent in June. The contract was first rejected in the summer of 2011 by 96 percent of voters.

The company basically gave its final offer in 2011 and hasn't budged since, while many workers have dug in on principle, figuring they've gone too far to give up the fight.

Unemployment benefits for Minnesota Crystal workers, which provided more than $1,000 a month for some, expired in October, tightening the economic vise. They had made $40,000 a year on average before overtime.

The lockout has hurt the company's bottom line, too, increasing operating costs. As replacement workers get more time on the job, though, Crystal Sugar — a farmer-owned cooperative — has said its operational efficiency has improved.

Now, however, the company is coping with significant declines in sugar prices. Crystal Sugar's fiscal 2013 payout to its farmer-members may be only $40 to $45 per ton, compared to a revised $63 a ton last year, according to a filing last week with federal securities regulators. That payout is affected by everything from sugar prices to crop size to plant efficiency.

As for the upcoming union vote, neither union nor company officials would hazard a guess on its outcome.

The union scheduled another vote after some workers expressed a desire for one, John Riskey, president of Bakery, Confectionery, Tobacco Workers and Grain Millers Local 167G, said in an interview Monday. "Members have asked," he said.

Moorhead-based Crystal Sugar, the largest U.S. beet sugar maker, locked out its 1,300 union workers after they rejected a contract that would have raised wages by 13 percent over five years, but would have significantly increased health care costs by transferring workers from a union plan to the company's health plan.

Also, union members rejected the broad "management rights" language in Crystal's offer, which would give management more discretion in workplace decisions, including promotions.

Since the lockout began, many workers have retired or quit, with many moving on to other jobs. About 640 have done so, said Crystal Vice President Brian Ingulsrud. That's up from 520 just before the last contract vote.

Crystal has plants in Moorhead, Crookston and East Grand Forks, Minn., as well as in Drayton and Hillsboro, N.D. The company first relied on Strom Engineering, a Minnetonka firm that specializes in supplying replacement workers in labor disputes.

Over time, the number of Strom workers has receded, though they have remained concentrated in skilled positions. Currently, 200 replacement workers are Strom employees, while the remaining 1,100 were hired directly by Crystal, Ingulsrud said.

Under federal labor law, locked-out workers are supposed to be rehired after a dispute has ended.