Deportation proceedings have begun for 20 of more than 50 suspected illegal migrant employees arrested on Thursday.
They were stopped near Leicester in coaches which were believed to be taking agency workers to food factories in Northamptonshire and Lincolnshire.
A total of 55 people were arrested and detained on suspicion of a range of immigration offences.
A Home Office spokeswoman said deportation proceedings were already under way for 20 of those arrested.
The operation, with 120 police and immigration officers, was carried out on the A6 near Oadby after the Home Office was tipped off by a recruitment company where staff were concerned about the number of foreign workers suspected of using fake documents.
The Home Office spokeswoman said those arrested included 35 men and 20 women.
A total of 41 of those held are believed to be Brazilian. Others are thought have come from Mongolia, Bolivia, Iraq and Iran.