26 U.S.C. § 6165: Bonds where time to pay tax or deficiency has been extended

In the event the Secretary grants any extension of time within which to pay any tax or any deficiency therein, the Secretary may require the taxpayer to furnish a bond in such amount (not exceeding double the amount with respect to which the extension is granted) conditioned upon the payment of the amount extended in accordance with the terms of such extension.