The investigation led to the revocation of the licences of AAW Contract Services, JDSS and EU Labour after the Gangmasters Licensing Authority (GLA) found overcrowded accommodation and workers living on less than £10 a day.
In a statement the GLA said they "uncovered a tangled web of exploitation where one gangmaster supplied the workers, another provided the accommodation and the transport, with the third believed to be a ‘lifeboat' licence that could be used to transfer the workers to if the other licences were revoked".
The decision was made following a multi-agency operation in Cornwall called Migrant Workers Action Week, involving Devon & Cornwall Constabulary, Kerrier & Penwith District Council, Cornwall County Fire Brigade and Vehicle & Operator Services Agency (VOSA).
The GLA found workers housed in overcrowded caravans and paid "subs" of £50 a week or less, with the rest of their wages held back until their contract had finished.
Workers who left AAW were not paid what they were owed and there was no evidence of forwarding addresses seen by GLA officers for the money to be sent to the workers.
GLA chairman Paul Whitehouse said: "Workers are not a commodity and should not be treated like one. The law is in place to protect them and we will enforce the law."
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