underpayment
(A)In the case of any failure by any person to pay on the date prescribed therefor any amount required by this section, there shall be imposed on such person a penalty of 10 percent of the underpayment. For purposes of the preceding sentence, the term “underpayment” means the excess of the amount of the payment required under this section over the amount (if any) of such payment paid on or before the date prescribed therefor. No penalty shall be imposed under this subparagraph on any failure which is shown to be due to reasonable cause and not willful neglect. (B)For purposes of part II of subchapter A of chapter 68, any payment required by this section shall be treated as a tax. (C)If any partnership or S corporation willfully fails to comply with the requirements of this section,shall cease to apply with respect to such partnership or S corporation. (g)The Secretary shall prescribe such regulations as may be necessary or appropriate to carry out the provisions of this section and section 280H, including regulations providing for appropriate adjustments in the application of this section andin cases where—