Immigration officers have arrested 11 people in what they describe as an intelligence-led operation.
The raid took place at Mappleborough Green near Alcester early on Wednesday and targeted gang masters and illegal workers, the immigration service said.
The 11 were arrested for alleged offences including staying longer than allowed in the UK and illegal entry.
The immigration service says nine are Indian and the nationality of the other two is still being determined.
Twelve other people who were already known to the service have been cautioned for working when they were legally not allowed to do so.