The Board may revoke an exemption, to the extent it specifies, when it finds that application in whole or in part of a provision of this part to the person, class, or transportation is necessary to carry out the transportation policy of
section 10101 of this title. The Board shall, within 90 days after receipt of a request for revocation under this subsection, determine whether to begin an appropriate proceeding. If the Board decides not to begin a proceeding to revoke a class exemption, the reasons for the decision shall be published in the Federal Register. Any proceeding begun as a result of a request under this subsection shall be completed within 9 months after it is begun.