I knew some corporations who had strong federal presence, more
   or less permanent government contracts [and the companies you
   mention are absolutely huge] did this, but I was thinking that
   most prison labor consists of road cleanup and "community
   service" type labor. But I hadn't considered that they are
   utilized in a "keep the money in the USA" way. [make use of
   Americans instead of foreigners" thing]. It is rather weird /
   disturbing to consider.