It shall be unlawful for any broker, dealer, or exchange, directly or indirectly, to make use of the mails or any means or instrumentality of interstate commerce for the purpose of using any facility of an exchange within or subject to the jurisdiction of the United States to effect any transaction in a security, or to report any such transaction, unless such exchange (1) is registered as national securities exchange under section 78f of this title, or (2) is exempted from such registration upon application by the exchange because, in the opinion of the Commission, by reason of the limited volume of transactions effected on such exchange, it is not practicable and not necessary or appropriate in the public interest or for the protection of investors to require such registration.
15 U.S. Code § 78e - Transactions on unregistered exchanges
(June 6, 1934, ch. 404, title I, § 5, 48 Stat. 885.)