Fraudulent tax evasion triggers a show-cause notice with interest and escalating penalties plus specified payment windows. Determination of tax unpaid, short paid, erroneously refunded or input tax credit wrongly availed by reason of fraud or wilful misstatement invokes a show-cause notice requiring payment of specified tax, interest under section 50 and a penalty equivalent to the tax; notices must be issued at least six months prior to the assessment time limit. Voluntary pre-notice payment with interest plus a fifteen per cent penalty prevents a notice; payment within thirty days of notice with interest and a twenty-five per cent penalty concludes that notice. Orders assessing tax, interest and penalty must be issued within five years of the annual return due date or erroneous refund, and payment within thirty days of the order with interest and a fifty per cent penalty concludes proceedings.