The commission and each commissioner, or the secretary of the commission may issue subpoenas and all necessary processes in proceedings pending before it; and each process shall extend to all parts of the state and may be served by any person authorized to serve processes of courts of record. Each witness who shall appear before the commission, or at a hearing before one of the individuals designated by it as provided in section 216B.15, or whose deposition is taken, shall receive for attendance the fees and mileage now provided for witnesses in civil cases in courts of record.