Up to 500 employees at IBM Corp’s Essex Junction, Vermont plant – it is the state’s largest private employer, will lose their jobs by the end of June. The company wants to buy out 300 to 500 permanent, full-time administrative, production and engineering workers at the plant. There are almost 6,600 workers at the plant, roughly 300 more than at the end of last year, after transfers from East Fishkill, New York.