Authorities have detained about 40 undocumented Myanmar migrant workers in the eastern Chinese province of Shandong after they complained to their embassy about forced unpaid labor at a seafood plant, while 60 others are still working there without pay, RFA reported.

The 100 laborers are among a pool of some 230,000 workers who’ve sought work in China in the wake of armed conflict, environmental destruction and natural disasters in Myanmar, the Mekong region’s largest source of migrants, according to the U.N.’s International Organization for Migration (IOM).