Except as otherwise provided by law or regulations, bonds or notes of the United States, or other obligations which are unconditionally guaranteed as to both interest and principal by the United States, may be pledged and deposited by principals as collateral security in lieu of bonds obtained from surety companies. Deposit of collateral security is governed by the provisions of 31 U.S.C. 9303 , and 31 CFR part 225.
27 C.F.R. § 17.104
Sec. 1, Pub. L. 97-258, 96 Stat. 1046 ( 31 U.S.C. 9301 , 9303 )