(a)      On the request of a party to a proceeding in which a hearing is required or held, the Commission shall issue subpoenas to compel the attendance and testimony of witnesses and the production of documents at a hearing or deposition to be taken by the party.

      (b)      On its own motion, the Commission may issue a subpoena to compel the attendance and testimony of witnesses and the production of documents at a hearing or deposition to be taken by the Commission.

      (c)      A subpoena shall be signed and issued by a commissioner or the Executive Secretary of the Commission.