The Interstate Commerce Act (Act) requires motor common carriers to publish their rates in tariffs filed with the Interstate Commerce Commission (ICC), 49 U.S.C. 10762, and prohibits both carriers and shippers from deviating from those rates, 10761. The Act also specifies that a carriers rates must be nondiscriminatory, 10741, and that its rates and practices must be reasonable, 10701, and charges the ICC, upon determining that a rate or practice violates the statute, with prescribing the rate or practice to be followed, 10704(b)(1). Purportedly pursuant to this authority, the ICC, in its recent Negotiated Rates decisions, has adopted a policy that relieves a shipper of the obligation to pay the filed rate when it has privately negotiated a lower rate with the carrier. From 1981 to 1983, Quinn Freight Lines, a motor common carrier and a subsidiary of petitioner Maislin Industries, U.S., Inc., privately negotiated interstate shipment rates with respondent Primary Steel, Inc., that were lower than Quinns filed rates. Quinn never file