MOORHEAD — Union members who have been locked out of American Crystal Sugar plants in Minnesota, Iowa and North Dakota for 20 months are heading back to work.

Just enough members changed their vote over the weekend to ratify the same contract they had rejected four times before. The union last voted in December when 55 percent of members voted to reject the company’s offer. This time, 55 percent agreed to the offer.

Nearly 1,300 members of the Bakery, Confectionery, Tobacco Workers and Grain Millers International union were locked out on Aug. 1, 2011, after rejecting the cooperative’s proposed contract. The company has operated the plants using replacement workers.

American Crystal is a Moorhead-based cooperative owned by about 2,800 sugar beet growers. It’s the nation’s largest sugar beet processor.