(a) If, after an exemption takes effect, changes in circumstances, including changes in law or policy, occur which call into question the continuing validity of the Department's original findings concerning the exemption, the Department may take steps to revoke or modify the exemption.

(b) Before revoking or modifying an exemption, the Department will publish a notice of its proposed action in the Federal Register and provide interested persons with an opportunity to comment on the proposed revocation or modification. Prior to the publication of such notice, the applicant will be notified of the Department's proposed action and the reasons therefore. Subsequent to the publication of the notice, the applicant will have the opportunity to comment on the proposed revocation or modification.

(c) Ordinarily the revocation or modification of an exemption will have prospective effect only.