220 ILCS 5/9-103
Subject to such rules and regulations as the Commission may prescribe, the schedules referred to in Section 9-102 shall be posted or kept on file in every office of a public utility where the public transacts business with such public utility. Any or all of such schedules kept as aforesaid shall be immediately produced by such public utility for inspection upon the demand of any person. A notice printed in bold type, in size prescribed by the Commission, stating that such schedules are on file with the agent and open to inspection by any person, and that the agent will assist any person to determine from such schedules any rates or other charges, classification, rules or regulations in force, shall be kept posted by the public utility in two public and conspicuous places in every such office. The form of every such schedule shall be prescribed by the Commission: Provided, that in lieu of filing the entire schedule in each office, any public utility may, subject to the regulations of the Commission, file or keep posted at such office, schedules of such rates or other charges, classifications, rules and regulations relating thereto, as are applicable at, to and from the place where such office is located.
The Commission may determine and prescribe the form in which the schedules required by this Act to be filed with the Commission and to be kept open to public inspection shall be prepared and arranged, and may change the form from time to time if it shall be found expedient.
220 ILCS 5/9-103