The existing anti-discrimination law that does not prohibit employers from discriminating based on whether or not the person is a smoker/nicotine user is a federal law.
ETA: Through the courts it was determined it is not discrimination if the person has a choice, unlike, skin color, disability... nicotine use is a choice just like alcohol and drug use which both of those can also ban you from employment without legal ramifications. I have been waiting for some time now for weight to come into full play, some are already testing those waters (since 2013) by charging their overweight employees higher insurance premiums.
The "Choice" position is a Very Slippery Slope.
Because the same argument can by applied to say Caffeine. Or perhaps eating or Not eating of Red Meat. Or the Taking or Not taking Daily Vitamins.
I wonder sometimes at What Point did the worth some put on the Dollar superseded the Values that we say this Country was Founded On?