26 C.F.R. § 1.6107-2
Form and manner of furnishing copy of return and retaining copy or record
(a) In general. The Commissioner may prescribe the form and manner of satisfying the requirements imposed by section 6107(a) and (b) and § 1.6107-1(a) and (b) in forms, instructions, or other appropriate guidance (see § 601.601(d)(2) of this chapter).
(b) Effective date. To the extent this section relates to section 6107(a) and § 1.6107-1(a), it applies to income tax returns and claims for refund presented to a taxpayer for signature after December 31, 2002. To the extent this section relates to section 6107(b) and § 1.6107-1(b), it applies after December 31, 2002, to returns and claims for refund for which the 3-year period described in section 6107(b) expires after December 31, 2002.