Legal Question in Administrative Law in Illinois

Since it is a voluntary organization, and smokers are not a protected class, then I would say yes, they can refuse membership to individuals who smoke.

I should reword my previous answer. No, they cannot make you quit smoking, but they do not have to allow you to remain a member if they prohibit smokers from being in their organization. All religions have various prohibitions. You need to decide if this particular habit is more or less important to you than being part of this particular organization.