386.390.  Complaint, who may make — procedure to hear — service of process, how had — time and place of hearing, how fixed. — 1.  Complaint may be made by the commission of its own motion, or by the public counsel or any corporation or person, chamber of commerce, board of trade, or any civic, commercial, mercantile, traffic, agricultural or manufacturing association or organization, or any body politic or municipal corporation, by petition or complaint in writing, setting forth any act or thing done or omitted to be done by any corporation, person or public utility in violation, or claimed to be in violation, of any provision of law subject to the commission's authority, of any rule promulgated by the commission, of any utility tariff, or of any order or decision of the commission; provided, that no complaint shall be entertained by the commission, except upon its own motion, as to the reasonableness of any rates or charges of any gas, electrical, water, sewer, or telephone corporation, unless the same be signed by the public counsel or the mayor or the president or chairman of the board of aldermen or a majority of the council, commission or other legislative body of any city, town, village or county, within which the alleged violation occurred, or not less than twenty-five consumers or purchasers, or prospective consumers or purchasers, of such gas, electricity, water, sewer or telephone service.

  2.  All matters upon which complaint may be founded may be joined in one hearing, and no motion shall be entertained against a complaint for misjoinder of causes of action or grievances or misjoinder or nonjoinder of parties; and in any review by the courts of orders or decisions of the commission the same rule shall apply with regard to the joinder of causes and parties as herein provided.

  3.  The commission shall not be required to dismiss any complaint because of the absence of direct damage to the complainant.  Upon the filing of a complaint, the commission shall cause a copy thereof to be served upon the public utility, corporation or person complained of.

  4.  Service in all hearings, investigations and proceedings pending before the commission may be made upon any person upon whom summons may be served in accordance with the provisions of the code of civil procedure of this state, and may be made personally or by mailing in a sealed envelope with postage prepaid.

  5.  The commission shall fix the time when and the place where a hearing will be had upon the complaint and shall serve notice thereof, not less than ten days before the time set for such hearing, unless the commission shall find that the public necessity requires that such hearing be held at an earlier date.