47 U.S.C. § 399b : US Code - Section 399B: Offering of certain services, facilities, or products by public broadcast station

    (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) of this section 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) of this section 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.