(b) if the Central Government is of opinion, in any case where the award has been given by a National Tribunal, that it will be inexpedient on public grounds affecting national economy or social justice to give effect to the whole or any part of the award, the appropriate Government, or as the case may be, the Central Government may, by notification in the Official Gazette, declare that the award shall not become enforceable on the expiry of the said period of thirty days.