17 CFR 170.2: Membership restrictions (section 17(b)(2) of the Act).

If it appears to the Commission to be necessary or appropriate in the public interest and to carry out the purposes of section 17 of the Act, a futures association may restrict its membership to individuals registered by the Commission in a particular capacity or to individuals doing business in a particular geographical region or to firms having a particular level of capital assets or which engage in a specified amount of business per year.