Six people were arrested on Friday, suspected of taking part in a scheme to recruit migrants from reception centers and put them to work illegally in the fields of southern Italy, police said.
The detentions in Calabria, mainland Italy's southwestern tip, were the first under new legislation meant to stamp out the exploitation of workers, many of them refugees, in the agriculture industry, the interior ministry said.
Police said the manager and two employees at a center were suspected of organizing the scheme with staff at agricultural firms.
Investigators found around 30 migrants, mainly Senegalese, Nigerian and Somali, each paid 15-20 euros ($22) a day off the books for 10-hour shifts picking potatoes and strawberries or minding livestock, the force said in a statement.
Interior Minister Marco Minniti said inspectors would visit all of Italy's reception centers over the next few days to check for any other cases.
"It is in our interest to guarantee the maximum transparency in the management of migrant centers," Minniti said.
Two of the suspects were held in custody, four placed under house arrest and another eight ordered to stay in the area, police said.
Anyone found guilty under the legislation brought in last year can be jailed for from one to six years and fined 500-1,000 euros for each worker recruited.