Any government debt will be collected almost any means necessary (in their eyes). This includes taking the amount owed directly from government pensions and/or bank accounts. My father, retired civil service and US Army, had this happen with a mistaken billing. They very quickly deducted the supposed amount owed from his pension without any notice.
if you are receiving compensation or pension, then it will be withheld until the debt is fullfil. If not, the bill will be send to the US Department of Treasure and futhermore, collections.