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With just days to go before two of Philadelphia's most prestigious hospitals refuse to hire smokers, the ban has relit a debate about the wisdom of regulating workers' behavior away from the workplace.

Both the highly rated University of Pennsylvania Health System, which includes the Hospital of the University of Pennsylvania, as well as the Children's Hospital of Philadelphia, named by US News and World Report as America's top children's hospital this year, will join dozens of hospitals across the country when they implement their policy on Monday, July 1.

The move has generated criticism among civil liberties activists, hospital employees and even doctors who fear that smokers will lie about their habit - and therefore become less likely to seek help in stopping it.

"It's not all slopes that are slippery, but this one really is," said Lewis Maltby, a former American Civil Liberties Union lawyer who now runs the National Workrights Institute in Princeton, N.J. He is critical of an employer's intrusion into the private time of employees.

"What you do in your own home on your own time is none of your boss's business unless it affects your work," he said.

Maltby noted that drinking alcohol, eating lots of junk food and not exercising are also bad for you. "Virtually everything you do in your private life affects your health," he said, wondering what other kinds of hiring restrictions could come to pass.

Desonia Mapp, 52, who has worked as a nursing assistant at the Hospital of the University of Pennsylvania for 13 years, said she was "dumbfounded. I couldn't believe they were doing this," she said as she took a cigarette break in the shade near bicycle racks outside the hospital last week. "If I drank, if I do whatever I do outside of the workplace, where does it end?" Mapp will not be affected by the new policy, which only applies to new hires.

Dr. Michael Siegel, a professor at the Boston University School of Public Health, also has serious doubts about the policy. "It is blatant employment discrimination," he said. "Employment decisions should be made based on a person's qualifications for a position.

"Once you step over that line and you start making decisions based on the group to which a person belongs that has no bearing on their actual qualifications, I think that's really dangerous," he said.

Ralph Muller, the chief executive of the sprawling University of Pennsylvania Health System, said the system was focusing on the health ills of smoking rather than issues like obesity because of the "50 years of science" behind smoking research.

The policy at Penn, with more than 28,000 employees, will extend to all of the university's health centers, including three large city hospitals, a center for advanced medicine, and six other clinics and medical practices. UPenn's clinics and offices in New Jersey will not be affected, because New Jersey is among 29 states and the District of Columbia that have passed smoker-protection laws preventing employers from discriminating against employees or job applicants because they do or do not smoke.

Penn and the children's hospital, which are affiliated but run as separate corporate entities, will have similar programs, with one exception. Penn will rely on an applicant's word on tobacco use, while the children's hospital will test applicants to determine if they're smokers. Those who admit to having started smoking after hiring would be offered a smoking-cessation program but would also have to pay higher health insurance premiums - about $30 more a month, said Robert Croner, senior vice president for human resources at the children's hospital, known locally as CHOP.

Whether the policy will shrink the available labor pool so that hospitals end up with vacancies they cannot fill does not seem to be much of an issue. CHOP has some 12,000 employees.

"It is something we have on our minds, but we don't think it will have that disruptive of an impact," Croner said of the applicant issue. According to the Centers for Disease Control (CDC), 43.8 million adults (19 percent) in the U.S. were smokers in 2011.

The Cleveland Clinic, with 42,000 employees, said that fears of a shrinking labor pool had proved unfounded when it became one of the first and biggest medical centers to impose its no-smokers policy in September of 2007.

"It really never reduced our pool," said Dr. Paul Terpeluk, the Cleveland Clinic's medical director for employee services.

Statistics on how many hospitals nationwide have the policy are hard to come by, but Boston's Siegel estimates the number at 50 to 60 health care systems around the country.

"I definitely believe it is a trend," he said. "It may reach the point where it is pretty much everybody doing this."