Illinois Statutes Chapter 220. Utilities § 5/15-506. Charges to conform to tariffs or schedules and orders of the Commission

(a) Overcharges and undercharges prohibited. No common carrier by pipeline shall offer, advertise, charge, demand, collect, or receive, in any manner, a greater, lesser, or different compensation for transportation or service in connection therewith than the rates and charges specified in tariffs or schedules on file with the Commission and in effect at the time the transportation or other service is rendered. No carrier shall offer, advertise, charge, demand, collect, or receive any compensation for transportation or other service rendered in connection therewith if there is not in effect at the time a lawfully applicable tariff or schedule. No carrier shall refund or remit, in any manner, or by any device, whether directly or indirectly, or through an agent or otherwise, other than or under Commission order, a portion of the rates or charges specified in tariffs or schedules on file with the Commission and in effect at the time. No carrier shall extend a discount, value, privilege, or facility for transportation or service rendered in connection therewith, except as specified in tariffs or schedules on file with the Commission and in effect at the time.

(b) Repayment of overcharges, collection of undercharges and reparations.