GLAA officers and Cambridgeshire Police carried out the operation at an address in Peterborough in the early hours of Thursday (11 July).
The suspect, a 50-year-old Romanian man, was interviewed by the GLAA before being released under investigation.
Three Romanian men, aged 45, 47 and 47, have been safeguarded and are now receiving support.
‘Safeguard the potential victims’
GLAA investigating officer Hayley Palmer said: “The operation was conducted after excellent work by our intelligence team, who acted swiftly to enable us to go to the address, make the arrest and safeguard the potential victims.
“There is no place in society for people who exploit others for their labour and we will not hesitate to work with partners to bring these offenders to justice and protect vulnerable workers.”
DCI Alan Page, Cambridgeshire Constabulary’s tactical lead for modern slavery and human trafficking, said: “Tackling modern slavery is a force priority and while we’re working hard to address it, we can’t do it alone.
“Increasing information in modern-day slavery and human trafficking is key to protecting the vulnerable.
‘The National Crime Agency’
“We work closely with partners, including the National Crime Agency and the GLAA.
“Slavery still exists in Cambridgeshire and it’s important that people are aware of the signs of modern slavery and human trafficking, and report any concerns to us.”
If you suspect someone is being exploited or is a victim of modern slavery, email or call the GLAA intelligence team on 0800 432 0804.
Meanwhile, two men who supplied workers to a food factory in Greater Manchester were last month fined for operating as unlicensed gangmasters.