About half of part-time employees who were eligible for employer-sponsored health care benefits last year signed up for the coverage, according to data from ADP Research Institute. That number could increase significantly next year when employers are required to provide health coverage to anyone working at least 30 hours per week. "I don't think employers will be surprised by this data. ... But the jury is still out on how they will respond," said Andrew Weber, CEO of the National Business Coalition on Health.