The commission shall supervise and regulate every motor carrier in this State and fix or approve the rates, fares, charges, classifications, and regulations pertaining to each motor carrier, except as provided in Section 58-23-20. The rates once established remain in effect until such time when, pursuant to complaint and proper hearing, the commission determines the rates are unreasonable. The commission may approve joint rates, local rates, and rate agreements between two or more motor carriers relating to rates, classifications, allowances, and charges agreed to and published by individuals, firms, corporations, or the Motor Truck Rate Bureau, Inc. Any of these agreements when approved by the commission are not in violation of Section 39-3-10.

As to holders of a certificate C the commission shall fix a maximum rate only.