We should recognize that the constitution still allows slavery as a punishment for crime. This is as much about slave labor, as it is about the prison industry receiving money from the public purse.
13th amendment
"Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
It's more like slave siphoning. Once someone is tagged as a criminal, there are seemingly endless ways to suck money from them, their families, the state, and the federal government. Each American indoctrinated into the criminal justice system in essence becomes that famous Duracell from the Matrix movie.
13th amendment "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
Good general overview of prison labor: http://thesocietypages.org/socimages/2013/04/04/prison-labor...
More detailed account of prison labor in Nevada regarding casinos and construction. http://vltp.net/casinos-prison-labor-strange-bedfellows/
The slave market: http://www.unicor.gov/
You can even get slave labor to operate your call center: http://www.unicor.gov/services/contact_helpdesk/