One concern voiced by groups like the National Workrights Institute is that such policies are a slippery slope  that if they prove successful in driving down health care costs, employers might be emboldened to crack down on other behavior by their workers, like drinking alcohol, eating fast food and participating in risky hobbies like motorcycle riding. The head of the Cleveland Clinic was both praised and criticized when he mused in an interview two years ago that, were it not illegal, he would expand the hospital policy to refuse employment to obese people.

“There is nothing unique about smoking,” said Lewis Maltby, president of the Workrights Institute, who has lobbied vigorously against the practice. “The number of things that we all do privately that have negative impact on our health is endless. If it’s not smoking, it’s beer. If it’s not beer, it’s cheeseburgers. And what about your sex life?”

Many companies add their own wrinkle to the smoking ban. Some even prohibit nicotine patches. Some companies test urine for traces of nicotine, while others operate on the honor system.

While most of the companies applied their rules only to new employees, a few eventually mandated that existing employees must quit smoking or lose their jobs. There is also disagreement over whether to fire employees who are caught smoking after they are hired. The Truman Medical Centers, here in Kansas City, for example, will investigate accusations of tobacco use by employees. In one recent case a new employee returned from a lunch break smelling of smoke and, when confronted by his supervisor, admitted that he had been smoking, said Marcos DeLeon, head of human resources for the hospital. The employee was fired.

Even antismoking advocates have found the issue tricky to navigate. The American Lung Association, the American Cancer Society and the World Health Organization do not hire smokers, citing their own efforts to reduce smoking.

But the American Legacy Foundation, an antismoking nonprofit group, has warned that refusing to hire smokers who are otherwise qualified essentially punishes an addiction that is far more likely to afflict a janitor than a surgeon. (Indeed, of the first 14 applicants rejected since the policy went into effect in October at the University Medical Center in El Paso, Tex., one was applying to be a nurse and the rest for support positions.)

“We want to be very supportive of smokers, and the best thing we can do is help them quit, not condition employment on whether they quit,” said Ellen Vargyas, chief counsel for the American Legacy Foundation. “Smokers are not the enemy.”