As many as 50,000 North Koreans have been sent abroad to work in conditions that amount to "forced labour", a UN investigator has said.
Marzuki Darusman said workers earn very little, are underfed and are sometimes forced to work up to 20-hour days.
Employers pay "significantly higher amounts" directly to the North Korean government, he said in his report.
The majority of the workers are in China and Russia, mainly in the mining, textile and construction industries.
But Mr Darusman, the special rapporteur on human rights in North Korea, also listed countries in Asia, Africa, the Middle East and Europe,
He said the companies who hire North Korean workers "become complicit in an unacceptable system of forced labour".
The workers are providing a source of hard currency to a country in a "really tight financial and economic situation".
He estimated that North Korea was earning $1.2bn-$2.3bn (£790m-£1.5bn) from the foreign worker system every year.
Since 2006, North Korea has been under international sanction for its nuclear weapons tests resulting in a shortage of foreign currency.