Commissioner discretion to reduce or waive tax penalties following voluntary, good-faith disclosure and cooperation. Section 273A grants the Commissioner discretion to reduce or waive penalties or specified interest and to stay or compound recovery where an assessee has voluntarily and in good faith made full and true disclosure of income or particulars, cooperated in enquiries, and paid or arranged payment of tax or interest; an explanation deems certain assessed excesses as constituting full disclosure. Board approval is required where aggregate penalties or the aggregate income subject to penalty exceed statutory thresholds, and a Board-approved order bars further relief for other assessment years; all orders under the section are final.