This is a good read on it:
Why Fruits and Veggies Are So Cheap in Chinatown - https://news.ycombinator.com/item?id=11981063 - June 2016 (237 comments)
The Kitchen Network: America’s Underground Chinese Restaurant Workers - https://news.ycombinator.com/item?id=8425246 - Oct 2014 (39 comments)