Hearings under this chapter may be held before the Commission, any member or members thereof, or any representative of the Commission designated by it, and appropriate records thereof shall be kept. In any proceeding before it, the Commission in accordance with such rules and regulations as it may prescribe, may admit as a party any interested State, State commission, municipality or any representative of interested consumers or security holders, or any competitor of a party to such proceeding, or any other person whose participation in the proceeding may be in the public interest.