It is discriminatory: you may NOT be barred from employment for a medical condition, such as tobacco (e.g. nicotine) additiction or dependence, and barring you from employment due to the use of tobacco products when you have such addiction or dependence (as most users have) can easily be found to be such illegal discrimination. They can have a policy barring smoking (or chewing or etc.) at work, and terminate you for violating that policy (legal, because you are being terminated for what you *do*, not for a condition), but they can't refuse to hire you for off-site, not-at-work, etc. use. If they refuse to hire you for this reason, you could contact the EEOC about possibly filing a disability (i.e. medical condition) discrimination complaint.