Sanction for issue of notice: specified authorities must approve reassessment notices based on time elapsed since assessment year. Substitution of section 151 prescribes the sanctioning authorities for issuance of reassessment notices: within a three year period sanction is by the Principal Commissioner/Principal Director or Commissioner/Director of Income tax; after that period sanction is by the Principal Chief Commissioner or Principal Director General or, if absent, the Chief Commissioner or Director General. The amendment ties approval level to time elapsed since the end of the relevant assessment year and takes effect from 1 April 2021.