39 CFR §273.9

1. (a)Any penalty or assessment imposed under the Program Fraud Civil Remedies Act may be recovered in a civil action brought by the Attorney General. In any such action, no matter that was raised or that could have been raised in a hearing conducted under part 962 of this title or pursuant to judicial review under 31 U.S.C. 3805 may be raised as a defense and the determination of liability and the determination of amounts of penalties and assessments shall not be subject to review. A civil action to recover a penalty or assessment shall be commenced within three years after the date on which the determination of liability for such penalty or assessment becomes final.
2. (b)The amount of any penalty or assessment which has become final may be collected by administrative offset in accordance with 31 U.S.C 3716, 3807.
3. (c)Any penalty or assessment imposed by the Postal Service under this part shall be deposited in the Postal Service Fund established by section 2003 of title 39.