1. Upon the complaint in writing of 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 by not less than twenty-five consumers or purchasers, or prospective consumers or purchasers of such gas, electricity, water or sewer, as to the illuminating power, purity, pressure or price of gas, the efficiency of the electric incandescent lamp supply, the voltage of the current supplied for light, heat or power, or price of electricity sold and delivered in such municipality, or the purity, pressure or price of water or the adequacy, sanitation or price of sewer service, the commission shall investigate as to the cause of such complaint.

2. When such complaint is made, the commission may, by its agents, examiners and inspectors, inspect the works, system, plant, devices, appliances and methods used by such person or corporation in manufacturing, transmitting and supplying such gas, electricity or water or furnishing said sewer service, and may examine or cause to be examined the books and papers of such person or corporation pertaining to the manufacture, sale, transmitting and supplying of such gas, electricity or water or furnishing of such sewer service.

3. The form and contents of complaints made as provided in this section shall be prescribed by the commission. Such complaints shall be signed by the officers, or by the customers, purchasers or subscribers making them, who must add to their signatures their places of residence, by street and number, if any.