220 ILCS 30/5
Each electric supplier is entitled, except as otherwise provided in this Act or (in the case of public utilities) the Public Utilities Act, to (a) furnish service to customers at locations which it is serving on the effective date of this Act, (b) furnish service to customers or premises which it is not now serving but which it had agreed to serve under contracts in existence on the effective date of this Act, and (c) resume service to any premises to which it has discontinued service in the preceding 12 months and on which are still located the supplier's service facilities.
Except as otherwise provided in this Act or (in the case of public utilities) the Public Utilities Act, no electric supplier may construct new lines, or extend existing lines, to furnish electric service to a customer or his premises which another electric supplier is entitled to serve, as provided in this Section, except with the written consent of such other electric supplier subject to the approval of the Commission as to such consent, if required.
This Section does not deprive an electric supplier of any right to furnish permanent service under a contract existing on the effective date of this Act to premises receiving temporary service from another supplier on the effective date of this Act.
Nothing in this Section prevents a generation and transmission electric cooperative from furnishing service to its member distribution electric cooperatives which are not incorporated municipalities.
220 ILCS 30/5