They went to an address on The Medway on the Grange estate, Daventry, last Thursday in response to a landlord’s concerns.
After an interview with the aid of Bulgarian interpreters, it was found the foreign nationals were being transported daily to work in another part of the district.
The action came after investigations by Daventry District Council (DDC) into over-occupation at a number of houses on its patch.
Sgt Sam Dobbs, from the police’s Safer Community Team said: “This kind of operation shows how effective agencies can be when we work together by sharing information and pooling the array of powers that are available to us.
“While police officers have many powers, the powers open to council officers and fire officers are also extensive, and we will use a combination of these to protect local residents, and those who are vulnerable.
“We are aware of the risks of foreign nationals being brought to the area to exploit the availability of work here, and we will make all efforts to ensure that those who do work here do so voluntarily and lawfully.
“I appeal to local people, housing owners and letting agents to report any concerns about over-occupation of local housing.
“This can also be done anonymously through Crimestoppers on 0800 555 111,” he added.
There are strict rules concerning houses of multiple occupancy designed to protect occupants from the risks of human trafficking or forced labour.
The people from the address in The Medway, who were interviewed by police, were being taken voluntarily to work and were in line with residence and employment rules.
Over-occupancy can place residents at risk of exploitation by landlords who sublet properties, breaching tenancy rules and be damaging to both property and the landlord.
This particular operation was carried out with the co-operation of the law-abiding landlord, and the agents who were acting for her.
The council’s health and housing portfolio holder Cllr Mike Warren said of the issue: “The 2004 Housing Act grants the council significant powers to ensure the housing provision in the district is safe and compliant with a range of requirements and regulations.
“DDC will not hesitate to investigate any concerns or complaints of potential unlawful housing provision and works closely with other agencies to keep local housing provision safe.”
Investigations are continuing. No arrests have been made.