26 CFR §20.6694-4

(a) In general. For rules relating to the extension of the period of collection when a tax return preparer who prepared a return or claim for refund for estate tax under chapter 11 of subtitle B of the Internal Revenue Code pays 15 percent of a penalty for understatement of the taxpayer's liability, and procedural matters relating to the investigation, assessment and collection of the penalties under sections 6694(a) and (b), the rules under § 1.6694-4 of this chapter will apply. (b) Effective/applicability date. This section is applicable to returns and claims for refund filed, and advice provided, after December 31, 2008.