The power to make rules under clause (c) of sub-section (2) of section 35 or clause (b) of section 36 shall include the power to make such rules or any of them retrospectively from a date not earlier than the date on which this Act received the assent of the President, but no such retrospective effect shall be given to any such rule so as to prejudicially affect the interests of any person to whom such rule may be applicable].