In an attempt to drive down health care costs, some employers have begun asking their employees whether they smoke. In some cases, employers are even considering asking smokers to pay more for health care.

But Ballard Spahr employee benefits attorney Edward I. Leeds said there is unresolved tension between supporting employers in their quest to lower health expenses, and protecting workers' privacy and preventing discrimination. "Those two aims are kind of jarring against each other right now," he said.

Mr. Leeds said the Health Insurance Portability and Accountability law, or HIPAA, which protects patient privacy, also prohibits unequal treatment based on illness or disability. "Under HIPAA, nicotine addiction is considered an adverse health condition," Mr. Leeds said. "That raises the question of whether employers are going to try to distinguish among employees who smoke, whether it's a choice to smoke, or whether it's a matter of being addicted to nicotine. No employer wants to get into that inquiry."