26 CFR §20.6107-1

(a) In general. A person who is a signing tax return preparer of any return or claim for refund of estate tax under chapter 11 of subtitle B of the Internal Revenue Code shall furnish a completed copy of the return or claim for refund to the taxpayer and retain a completed copy or record in the manner stated in § 1.6107-1 of this chapter. (b) Effective/applicability date. This section is applicable to returns and claims for refund filed after December 31, 2008.