26 U.S.C. § 2207B

(a) Estate tax (1) In general If any part of the gross estate on which tax has been paid consists of the value of property included in the gross estate by reason of section 2036 (relating to transfers with retained life estate), the decedent’s estate shall be entitled to recover from the person receiving the property the amount which bears the same ratio to the total tax under this chapter which has been paid as— (A) the value of such property, bears to (B) the taxable estate. (2) Decedent may otherwise direct Paragraph (1) shall not apply with respect to any property to the extent that the decedent in his will (or a revocable trust) specifically indicates an intent to waive any right of recovery under this subchapter with respect to such property. (b) More than one recipient For purposes of this section, if there is more than 1 person receiving the property, the right of recovery shall be against each such person. (c) Penalties and interest In the case of penalties and interest attributable to the additional taxes described in subsection (a), rules similar to the rules of subsections (a) and (b) shall apply. (d) No right of recovery against charitable remainder trusts No person shall be entitled to recover any amount by reason of this section from a trust to which section 664 applies (determined without regard to this section).