MATTHEW BROWNBILLINGS, Mont. (AP) â¿¿ With dozens of workers set to be laid off early next year, a southeastern Montana coal mine faces an uncertain future as an internal ownership dispute and the impending loss of a key customer leaves roughly 90 more jobs hanging in the balance. The Decker Coal Mine near the Wyoming border was once among the largest surface mines in the U.S., producing more than 10 million tons of the fuel annually. But with production volumes down to less than a third of that amount, mine managers have announced up to 75 workers will lose their jobs in mid-January. Mine representatives have declined to say how long Decker will stay operational. Court documents reviewed by The Associated Press suggest mining could end as soon as the end of 2013. Union leaders for many of the mine's 162 workers have yet to be told exactly how many jobs will be lost in January and whether more could follow, said Mike Dalpaiz, vice president of United Mine Workers of America. "We have made requests to the employers to give us all the documents so we can make heads or tails of it and try to help out our people. As of today we have nothing," Dalpaiz said Tuesday. Court documents filed in a federal lawsuit reveal the mine's fate could hinge on the outcome of an internal dispute between the mine's co-owners â¿¿ subsidiaries of Australian coal start-up Ambre Energy and Wyoming-based Cloud Peak Energy. Decker's contract with major customer Detroit Edison Company expires next year, according to those documents. Cloud Peak's attorneys said coal production will cease with the end of that contract, with any remaining workers shifted into mine reclamation duties. However, Ambre has signaled it wants to keep mining at Decker as part of its aspiration to tap into the growing coal export market. The company, which co-owns a second mine in Wyoming with Anadarko Petroleum, in April announced a deal to supply up to 5.5 million tons of coal per year to a pair of utilities in South Korea.