27 CFR § 70.91
Interest on erroneous refund recoverable by suit
April 24, 2020
Any portion of an internal revenue tax (or any interest, assessable penalty, additional amount, or addition to tax) which has been erroneously refunded, and which is recoverable by a civil action pursuant to 26 U.S.C. 7405, shall bear interest at the underpayment rate referred to in §70.93 of this part.
[T.D. ATF-301, 55 FR 47614, Nov. 14, 1990]