Penalties for failure to pay tax at the time required, for willful refusal to pay the tax and for fraudulent nonpayment of tax are provided for in 26 U.S.C. 5661 and 6656. In addition to these penalties, there is a penalty for the delinquent filing of a tax return, imposed as an addition to the tax shown on the return, amounting to five percent for each month or fraction thereof of the delinquency, not exceeding 25 percent in the aggregate, unless it is shown that the delinquency is due to reasonable cause and not to willful neglect.

(Sec. 201, Pub. L. 85-859, 72 Stat. 1407, as amended, 1410, as amended (26 U.S.C. 5661, 5684, 6651, 6656))