31 C.F.R. § 256.22
The setoff statute establishes a two-step process to collect debts that are owed to the United States. If an agency notifies Fiscal Service of a debt for which a court has issued a judgment against a debtor in favor of the United States, or for which the IRS has issued a tax levy pursuant to 26 U.S.C. 6331 , then Fiscal Service will automatically set off the debt from the payment. If the debt owed to the United States has not been judicially determined, then Fiscal Service must notify the claimant of the debt and request the debtor's consent to a setoff. If the debtor consents, then Fiscal Service will set off the debt. If the debtor does not consent, then Fiscal Service will withhold from payment an amount equal to the debt. Fiscal Service also may withhold an amount sufficient to pay the cost of litigating the debt to judgment. Fiscal Service then will consult with the underlying agency and the Department of Justice regarding the necessity for a civil action to reduce the debt to judgment. If litigation proceeds and is successful, Fiscal Service will set off the debt. If the suit is unsuccessful, Fiscal Service will pay the withheld amount with interest accruing from the date when payment would have been made.
31 C.F.R. §256.22