https://www.aclu.org/news/human-rights/captive-labor-exploit...
It also doesn't say that they report being compelled to work. It says they receive benefits from working that they don't receive without working. The fact that voluntary workers get their sentences reduced doesn't convert them into involuntary workers.
Trying to spin this as benefits is...odd:
"they are required to work or face additional punishment such as solitary confinement, denial of opportunities to reduce their sentence, and loss of family visitation."
"Denial of opportunities to reduce their sentence" means that prisoners with jobs are considered to be better candidates for sentence reduction by various means. That's true, but it doesn't come anywhere near "being compelled to work".
The ACLU doesn't provide any numbers on who reports being compelled to work. They provide a large number that includes some things that qualify as coercion and some that are entirely innocuous. This is the "prison forced labor" analogue of reporting that large majorities of female undergraduates suffer sexual assault on campus, where the definition of sexual assault includes "unwelcome sexual remarks".