Employment Law Questions? Ask an Employment Lawyer.
Yes, a person can be terminated for being a smoker because smoking is not a protected class, unlike race, religion, gender, age, disability or recent FMLA use. Those classes have a statute which specifically makes it illegal to terminate someone based on that, but being a smoker is not protected in that way.
So, the only way an employee could be protected in that situation is if they had an employment contract that they signed which stated they could only be terminated for "cause" and the definition of cause didn't include being a smoker.