Two men and two women arrested this morning on Deeside in Flintshire, in an investigation into human trafficking and the exploitation of workers, have been released on bail until June.
North Wales Police have said they had concerns about "more than 30" workers from Poland, in their investigation into human trafficking and the exploitation of workers in Flintshire.
Two men and two women suspected of being gangmasters have been arrested.
British Red Cross volunteers have provided support to 12 workers, after an operation this morning in Flintshire in which four people were arrested in an investigation into human trafficking and the exploitation of workers.
The Red Cross gave practical help, including food and drinks, and emotional support, and volunteers stayed at a rest centre that was set up until alternative arrangements had been made for the people affected.
North Wales Police Detective Inspector Dave Speed said: "Four people have been arrested, while the British Red Cross and the Salvation Army have set up reception centres for the workers.”
North Wales Police is working the Serious Organised Crime Agency, The Gangmasters Licensing Authority, the Red Cross and the Salvation Army to look into whether foreign workers in the Deeside area have been trafficked or exploited.
Four people have been arrested in Flintshire by police investigating human trafficking and the exploitation of workers.
The arrests were made this morning, and the people are being questioned at Wrexham Police Station.