"Slavery 400 years ago, slavery today. It's the same, but with a new name. They're practicing slavery under color of law." (Ruchell Cinque Magee)
The 13th Amendment to the U.S. Constitution retained the right to enslave within the confines of prison. “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.” Dec. 6, 1865.
Even before the abolition of chattel slavery, America's history of prison labor had already begun in New York's State Prison at Auburn soon after it opened in 1817. Auburn became the first prison that contracted with a private business to operate a factory within its walls. Later, in the post Civil War period, the "contract and lease" system proliferated, allowing private companies to employ prisoners and sell their products for profit.
Today, such prisons are referred to as “Factories with Fences.” (/www.unicor.gov/information/publications/pdfs/corporate/CATMC1101_C.pdf)