Starting in January, the Affordable Care Act will require businesses with 50 or more full-time-equivalent employees to offer workers health insurance or face penalties that can exceed $2,000 per employee. The health care law’s employer mandate, a provision that business groups fought against fiercely, is intended to make affordable health insurance available to more people by requiring employers to bear some of the cost of providing it. For some business owners on the edge of the cutoff, the mandate is forcing them to weigh very carefully the price of growing bigger.