26 CFR 1.501(c)(8)-1: (c)(8)-1 Fraternal beneficiary societies.

(a) A fraternal beneficiary society is exempt from tax only if operated under the lodge system or for the exclusive benefit of the members so operating. Operating under the lodge system means carrying on its activities under a form of organization that comprises local branches, chartered by a parent organization and largely self-governing, called lodges, chapters, or the like. In order to be exempt it is also necessary that the society have an established system for the payment to its members or their dependents of life, sick, accident, or other benefits.