Where the Central Government is of the opinion that it is necessary or expedient in the public interest so to do, it may, by notification in the Official Gazette and subject to such conditions, if any, as it may specify in the notification,--
         (a) exempt any person or class of persons from the operation of all or any of the provisions of this Act or the rules made thereunder; and
         (b) as often as may be, cancel any such notification and again subject, by a like notification, the person or class of persons to the operation of such provisions.