Notwithstanding anything contained in this Act, if the Central Government is of opinion that in respect of any metallurgical factory or class of metallurgical factories the levy of the duty of customs or duty of excise on iron ore or manganese ore¹[or chrome ore] under this Act is disproportionate to the cost of collection of such duty of customs or duty of excise from such metallurgical factory or class of metallurgical factories, it may, by notification in the Official Gazette and subject to such exceptions and modifications as may be specified in the said notification, exempt such metallurgical factory or class of metallurgical factories from all or any of the provisions of this Act.