About a third of U.S. companies could find themselves inviolation of a provision of the recently enacted healthcare reformmeasure because some of their employees might not able to affordthe health care coverage they provide, according to an analysis byhuman resources consultancy Mercer.

The Patient Protection and Affordable Care Act (PPACA) defines“affordable” health insurance as coverage that costs employees nomore than 9.5% of their household income. Using data from its 2009survey of nearly 3,000 employers that sponsor health plans, Mercerestimates that 38% of the companies have some employees for whomhealth coverage would be unaffordable. Bigger employers are inbetter shape, but not immune; 20% of companies with 20,000 or moreemployers would have a problem.

Those percentages probably overstate the extent of the problem,Mercer says, because its data includes only average employeesalaries, not total household income. “What's troubling is it willbe hard for employers to anticipate even whether it's a problem,because they're missing that piece of information about thehousehold income,” says Beth Umland, Mercer's director of researchfor health and benefits. “So they're doing more conservativeestimates based on what they're paying the employee.”