Discriminating against people who smoke?!? What about discriminating against people who don't smoke?!?! They can't go into a bar without inhaling smoke, which isn't healthy, and just isn't pleasant. Even cigarette ashes turn my stomach.
Although I don't think it is "discrimination" by any means, I should say that it would be the government discriminating against smokers, which isn't permissable. It may be reprehensible for me to discriminate against you, but it should be permited. The government, however, is a different story.