Rulemaking power limits retrospective notice requirement after searches by allowing rules to exempt classes from six year notices. The amendment authorises the Central Government to make rules specifying classes of cases in which the Assessing Officer shall not be required to issue notice for assessing or reassessing the total income for the six assessment years immediately preceding the assessment year in which a search is conducted or requisition is made, except where any assessment or reassessment has abated under the second proviso.