About one-third of the employees working at a Caterpillar Inc. facility in South Milwaukee will be laid off as a result of slackening demand for mining equipment, according to a company announcement. Of the plant’s total workforce of approximately 800 employees, 260 will be laid off. Caterpillar, a construction and mining equipment manufacturer, had recently signed a new six-year contract with United Steelworkers union Local 1343.