slave labour 
noun [mass noun]
Labour which is coerced and inadequately rewarded, or people that do it: most of production is carried out by slave labour...
- But the implication that Europeans were indifferent to the colour of their slaves rests on an equivocation between unfree labour and slave labour.
- It cannot compete against regimes that tolerate slave labour or forced child labour.
- Some owners bluntly told their slaves they did not want the financial burden of women and children without the reward of cheap slave labor.