The Thirteenth Amendment abolished slavery and involuntary servitude except as a punishment for crime.
Make no mistake, those "volunteers" are modern day slaves. They may have the blessing of the Constitution, but they're slaves nonetheless. Colorado actually just officially outlawed it last week.[2] A few other sources:
- https://www.nytimes.com/2018/08/30/opinion/national-prison-s...
- https://www.huffingtonpost.com/entry/prison-strike-modern-da...
- https://eji.org/history-racial-injustice-prison-labor
[1] 18 U.S. Code § 1589
[2] https://www.vox.com/policy-and-politics/2018/11/6/18056408/c...