Complaint may be made by the commission of its own motion or by 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 public utility including any rule, regulation or charge heretofore established or fixed by or for any public utility, in violation, or claimed to be in violation of any provision of law or of any order or rule of the commission: provided, that no complaint shall be entertained by the commission, except upon its own motion, as to the reasonableness of any rate or charges of any gas, electrical, water or telephone corporation, unless the same be signed by the mayor or the president or chairman of the board of trustees or a majority of the council, commission or other legislative body of the city or county or city or town, if any, within which the alleged violation occurred, or not less than 25 consumers or purchasers or prospective consumers or purchasers of such gas, electricity, water or telephone service.