The article I linked to claims that the language of the amendment bars legal challenges to unpaid or minimally paid prison labor. (It also mentions the book you mentioned.) The Thirteenth Amendment which is ostensibly about slavery would seem to ban prison labor outside of prisons. That’s the connection I wanted to make. Is there something to that?

I know that I’m casting a wide net. Prison labor is certainly not the same as slavery as it existed in the US decades ago. I do think, though, that I’m at least somewhat justified in calling prison labor slavery. Prisoners are forced to do it and they are not paid or paid very little. (This is not necessarily a moral judgment. Just because something meets some definition doesn’t mean it’s wrong.)