Three men, aged 53, 38 and 20 years old from the St Brides area of Newport, have been arrested on suspicion of slavery and servitude offences, Gwent Police said.
Four other suspects remain in custody and are assisting officers with their enquiries after the granting of a further 24 hours in custody by a District Judge.
More top news
Theresa May will tell European counterparts their shared political legacies depend on agreeing a good Brexit deal.
What does Theresa May's request for a couple of years of "transition" to full Brexit mean for Britain the the EU?
Mexico's navy says there are no missing children at a collapsed school where rescuers have been hunting for a trapped girl.