The workers who work at the plants that I visited are "free labor" in that they chose to work there for wages.
Contrary to Bircher propaganda, most of the folks who work in factories in China are paid wages and are free to work wherever they can find a job. Most factories in China are owned by private individuals, many of whom are part of the Chinese diaspora in Hong Kong, Singapore, Malaysia, etc.
There are factories in the prisons in China, but most of the goods produced go to the military or to the domestic market, not for export.
Well since you missed the point I'll repeat it for you. The chicoms do not pay enough wages for their laborers to buy foreign made goods. The chicoms do not like money exiting their borders. The minimal wages the pay ensure that the products they produce are inexpensive and that their workers can only afford domestic goods. How many factory workers did you see with Levi jeans, Nike shoes, or a Cadillac SUV?
The difference between free and slave labor is that slaves are given clothing, housing and food. Free labor gets nothing at all except the privilege of working for the state and not being imprisoned. Free labor has to provide for itself all the things slaves receive.