26 C.F.R. § 1.501(c)(6)-1
A business league is an association of persons having some common business interest, the purpose of which is to promote such common interest and not to engage in a regular business of a kind ordinarily carried on for profit. It is an organization of the same general class as a chamber of commerce or board of trade. Thus, its activities should be directed to the improvement of business conditions of one or more lines of business as distinguished from the performance of particular services for individual persons. An organization whose purpose is to engage in a regular business of a kind ordinarily carried on for profit, even though the business is conducted on a cooperative basis or produces only sufficient income to be self-sustaining, is not a business league. An association engaged in furnishing information to prospective investors, to enable them to make sound investments, is not a business league, since its activities do not further any common business interest, even though all of its income is devoted to the purpose stated. A stock or commodity exchange is not a business league, a chamber of commerce, or a board of trade within the meaning of section 501(c)(6) and is not exempt from tax. Organizations otherwise exempt from tax under this section are taxable upon their unrelated business taxable income. See part II (section 511 and following), subchapter F, chapter 1 of the Code, and the regulations thereunder.
26 C.F.R. §1.501(c)(6)-1