Working conditions for migrants in Cornwall are to be checked out by police and council inspectors following a survey that revealed 74% of local employers would suffer without them.
An estimated 50,000 people from other European states now live and work in the South West of England.
A survey by Penzance Job Centre of 500 employers revealed a large proportion relied heavily on migrant workers.
Three-quarters claimed their firms would suffer or shut down completely without migrant labour.
Devon and Cornwall Police said if the area was not an attractive place to work for migrant labour, then local industries could suffer.
He told BBC News: “We’ve had some intelligence in to say that some of the sites we’re planning to visit are housing migrant workers in ways that you or I would not want to be housed.”