17 CFR 240.10b-3: b-3 Employment of manipulative and deceptive devices by brokers or dealers.

(a) It shall be unlawful for any broker or dealer, directly or indirectly, by the use of any means or instrumentality of interstate commerce, or of the mails, or of any facility of any national securities exchange, to use or employ, in connection with the purchase or sale of any security otherwise than on a national securities exchange, any act, practice, or course of business defined by the Commission to be included within the term “manipulative, deceptive, or other fraudulent device or contrivance”, as such term is used in section 15(c)(1) of the act.

(b) It shall be unlawful for any municipal securities dealer directly or indirectly, by the use of any means or instrumentality of interstate commerce, or of the mails, or of any facility of any national securities exchange, to use or employ, in connection with the purchase or sale of any municipal security, any act, practice, or course of business defined by the Commission to be included within the term “manipulative, deceptive, or other fraudulent device or contrivance,” as such term is used in section 15(c)(1) of the act.