Donna Baker of Adrian, Mich., owns an accounting firm, payroll company and retail store. Her husband, Kim, is the sixth generation owner of a dairy farm. While the four businesses are separate entities, they count as one employer under the health-care law due to a technicality — Mrs. Baker is a minority stakeholder in the 1,800-acre property that her husband’s farm sits on, plus she helps out with some of the farm’s bookkeeping. As a result, the Bakers are subject to aggregation rules in the U.S. tax code, which means they would be required to offer health-insurance benefits to their...