Small employers cannot buy health insurance unless 75 percent of workers offered coverage enroll. Under Senator McCain's proposal to replace the tax exclusion for employer-sponsored insurance (ESI) with tax credits usable for ESI or non-group plans, many young and healthy workers would save money by shifting from ESI to non-group coverage; non-group plans typically lower premiums for healthy enrollees. Some employers could no longer meet participation requirements and would become unable to buy group insurance. Many of their employees would involuntarily lose ESI, forcing them into the non-group market, where older workers and those with health problems may fare poorly.