26 C.F.R. § 1.6662-1
Section 6662 imposes an accuracy-related penalty on any portion of an underpayment of tax required to be shown on a return that is attributable to one or more of the following:
Sections 1.6662-1 through 1.6662-5 address only the first three components of the accuracy-related penalty, i.e., the penalties for negligence or disregard of rules or regulations, substantial understatements of income tax, and substantial (or gross) valuation misstatements under chapter 1. The penalties for disregard of rules or regulations and for a substantial understatement of income tax may be avoided by adequately disclosing certain information as provided in § 1.6662-3(c) and §§ 1.6662-4(e) and (f) , respectively. The penalties for negligence and for a substantial (or gross) valuation misstatement under chapter 1 may not be avoided by disclosure. No accuracy-related penalty may be imposed on any portion of an underpayment if there was reasonable cause for, and the taxpayer acted in good faith with respect to, such portion. The reasonable cause and good faith exception to the accuracy-related penalty is set forth in § 1.6664-4 .
26 C.F.R. §1.6662-1