41 U.S.C. § 4503

Advance payments under section 4501 of this title may be made only on adequate security and a determination by the agency head that to do so would be in the public interest. The security may be in the form of a lien in favor of the Federal Government on the property contracted for, on the balance in an account in which the payments are deposited, and on such of the property acquired for performance of the contract as the parties may agree. This lien shall be paramount to all other liens and is effective immediately upon the first advancement of funds without filing, notice, or any other action by the Federal Government.