Presumably China has also convicted it's forced labor of some crimes as well.

Regardless of what the laws are, I believe that prison labor is a bad practice with big ethical issues—it incentives incarceration as a means to procure cheap/free labor that can be used to turn a profit for those in power.

EDIT: To clarify: I don't think giving prisoners an option to work is a bad thing, but nobody should be allowed to profit off of such labor other than the prisoner themselves. Anything else tends to lead towards undesirable incentives and outcomes.