Mandatory penalty for duty or interest shortfall applies, with reduced liability if dues and interest are paid promptly after determination. Section 114A fixes a mandatory penalty equal to the duty or interest determined where there is collusion, willful misstatement or suppression leading to short levy or erroneous refund; payment of the determined duty or interest and applicable interest within thirty days of communication reduces the penalty, and appellate alterations of duty or interest govern penalty recalculation and the availability of the reduced penalty, with prior payments adjusted against total liability and a bar on invoking other overlapping penalty provisions.