69-12-603. Investigation of operation under agreement. The commission may, upon complaint or upon its own initiative without complaint, investigate and determine whether any agreement previously approved by it under 69-12-601 or any terms or conditions upon which such approval was granted are not in conformity with 69-12-601 and 69-12-602 or whether any such terms or conditions are not necessary for the purpose of conformity with 69-12-601 and 69-12-602. After such investigation, the commission may by order terminate or modify its approval of such agreement if it finds such action necessary to insure conformity with 69-12-601 and 69-12-602 and may modify the terms and conditions upon which such approval was granted to the extent it finds necessary to insure conformity with 69-12-601 and 69-12-602 or to the extent it finds its terms and conditions unnecessary to insure such conformity. The effective date of any order terminating or modifying approval or modifying terms and conditions may be postponed for such period as the commission determines is reasonably necessary to avoid undue hardship.