47 U.S.C. § 399b

(a) “Advertisement” defined For purposes of this section, the term “advertisement” means any message or other programming material which is broadcast or otherwise transmitted in exchange for any remuneration, and which is intended— (1) to promote any service, facility, or product offered by any person who is engaged in such offering for profit; (2) to express the views of any person with respect to any matter of public importance or interest; or (3) to support or oppose any candidate for political office. (b) Offering of services, facilities, or products permitted; advertisements prohibited (1) Except as provided in paragraph (2), each public broadcast station shall be authorized to engage in the offering of services, facilities, or products in exchange for remuneration. (2) No public broadcast station may make its facilities available to any person for the broadcasting of any advertisement. (c) Use of funds from offering services, etc. Any public broadcast station which engages in any offering specified in subsection (b)(1) may not use any funds distributed by the Corporation under section 396(k) of this title to defray any costs associated with such offering. Any such offering by a public broadcast station shall not interfere with the provision of public telecommunications services by such station. (d) Development of accounting system Each public broadcast station which engages in the activity specified in subsection (b)(1) shall, in consultation with the Corporation, develop an accounting system which is designed to identify any amounts received as remuneration for, or costs related to, such activities under this section, and to account for such amounts separately from any other amounts received by such station from any source.