Police and immigration officials have made 36 arrests during raids in Northamptonshire and Lincolnshire. At a number of addresses in Northampton, 13 suspected illegal workers - among them Poles and Latvians - were picked up at 0600 GMT on Thursday.
They had allegedly been working for construction companies in the town.
Later on Thursday morning, officials from the Department for Work and Pensions, together with police and immigration staff, raided a packing warehouse in Spalding in Lincolnshire.
They made 23 arrests there, involving suspected illegal workers from eastern Europe.