Sailfish2. Read this:
NORTH KOREAN FORCED LABOUR IN THE EU, THE POLISH CASE: HOW THE SUPPLY OF A CAPTIVE DPRK WORKFORCE FITS OUR DEMAND FOR CHEAP LABOUR
Page 44 
 “To be eligible as a foreign labourer, you have to be formally married and your children have to remain in back home in North Korea—they are hostages to prevent you from escaping. Your formally recognized marriage has to be amicable and when you officially get dispatched overseas, the president of a neighbourhood association and three colleagues have to guarantee [your good behaviour].”
http://slavestothesystem.eu/wp-content/uploads/2016/07/North-Korean-Forced-Labour-in-the-EU-the-Polish-Case.pdf