26 U.S.C. § 6602 : US Code - Section 6602: Interest on erroneous refund recoverable by suit

Search 26 U.S.C. § 6602 : US Code - Section 6602: Interest on erroneous refund recoverable by suit

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 suit
pursuant to section 7405, shall bear interest at the underpayment
rate established under section 6621 from the date of the payment of
the refund.