220 ILCS 5/8-503
Whenever the Commission, after a hearing, shall find that additions, extensions, repairs or improvements to, or changes in, the existing plant, equipment, apparatus, facilities or other physical property of any public utility or of any 2 or more public utilities are necessary and ought reasonably to be made or that a new structure or structures is or are necessary and should be erected, to promote the security or convenience of its employees or the public or promote the development of an effectively competitive electricity market, or in any other way to secure adequate service or facilities, the Commission shall make and serve an order authorizing or directing that such additions, extensions, repairs, improvements or changes be made, or such structure or structures be erected at the location, in the manner and within the time specified in said order; provided, however, that the Commission shall have no authority to order the construction, addition or extension of any electric generating plant unless the public utility requests a certificate for the construction of the plant pursuant to Section 8-406 and in conjunction with such request also requests the entry of an order under this Section. If any additions, extensions, repairs, improvements or changes, or any new structure or structures, which the Commission has authorized or ordered to be erected, require joint action by 2 or more public utilities, the Commission shall notify the said public utilities that such additions, extensions, repairs, improvements or changes or new structure or structures have been authorized or ordered and that the same shall be made at the joint cost whereupon the said public utilities shall have such reasonable time as the Commission may grant within which to agree upon the apportionment or division of cost of such additions, extensions, repairs, improvements or changes or new structure or structures, which each shall bear. If at the expiration of such time such public utilities shall fail to file with the Commission a statement that an agreement has been made for a division or apportionment of the cost or expense of such additions, extensions, repairs, improvements or changes, or new structure or structures, the Commission shall have authority, after further hearing, to make an order fixing the proportion of such cost or expense to be borne by each public utility and the manner in which the same shall be paid or secured.
Nothing in this Act shall prevent the Commission, upon its own motion or upon petition, from ordering, after a hearing, the extension, construction, connection or interconnection of plant, equipment, pipe, line, facilities or other physical property of a public utility in whatever configuration the Commission finds necessary to ensure that natural gas is made available to consumers at no increased cost to the customers of the utility supplying the gas.
Whenever the Commission finds, after a hearing, that the public convenience or necessity requires it, the Commission may order public utilities subject to its jurisdiction to work jointly (1) for the purpose of purchasing and distributing natural gas or gas substitutes, provided it shall not increase the cost of gas to the customers of the participating utilities, or (2) for any other reasonable purpose.
220 ILCS 5/8-503