26 USC 6653 - Failure to pay stamp tax

Any person (as defined in section 6671 (b)) who
(1) willfully fails to pay any tax imposed by this title which is payable by stamp, coupons, tickets, books, or other devices or methods prescribed by this title or by regulations under the authority of this title, or
(2) willfully attempts in any manner to evade or defeat any such tax or the payment thereof,

shall, in addition to other penalties provided by law, be liable for a penalty of 50 percent of the total amount of the underpayment of the tax.