Whenever a certificate of public convenience and necessity has been issued to a gas distribution system and a controversy arises as to whether an extension of service should or should not be made within the territory included in the certificate, the commission shall have jurisdiction to determine whether or not such extension shall be made and, if so, upon what terms. In making this determination, the commission shall consider the economic feasibility of that particular extension and the supply of gas available therefor. This Code section shall not apply to extensions of gas distribution systems by municipalities and counties of this state.