(a) There is no obligation upon a carrier to extend unsecured credit for interstate and foreign communication services to a candidate or person on behalf of such candidate for Federal office. However, if the carrier chooses to extend such unsecured credit, it shall comply with the requirements set forth in paragraphs (b) through (g) of this section.

(b) If a carrier decides to extend unsecured credit to any candidate for Federal office or any person on behalf of such candidate, then unsecured credit shall be extended on substantially equal terms and conditions to all candidates and all persons on behalf of all candidates for the same office, with due regard for differences in the estimated quantity of service to be furnished each such candidate or person.