Undisclosed income return filing attracts graded punishment based on tax amount and wilful non-compliance. Wilful failure to furnish, within the prescribed time, the return of income disclosing undisclosed income for the block period, when required by notice, attracts prosecution and graded punishment based on the amount of tax involved. The punishment may extend to imprisonment up to two years, imprisonment up to six months, or fine alone, depending on whether the tax exceeds fifty lakh rupees, exceeds ten lakh rupees but does not exceed fifty lakh rupees, or falls in any other case.