The amount of any penalty or assessment which has become final, or for which a judgment has been entered under §308.541 or §308.542 of this subpart, or any amount agreed upon in a compromise or settlement under §308.545 of this subpart, may be collected by administrative offset under 31 U.S.C. 3716, except that an administrative offset may not be made under this section against a refund of an overpayment of federal taxes, then or later owing by the United States to the defendant.