Nine gangmasters who supplied hundreds of workers to pick flowers and vegetables in Cornwall have violated standards, an investigation has found.
The aim of the GLA is to protect migrant workers from exploitation
The Gangmasters Licensing Authority (GLA) said a number of licences will now be revoked following the investigation into pay and conditions.
Violations included paying below the minimum wage, excessive accommodation charges and using faulty minibuses.
Exploited workers were mainly Polish, Lithuanian, Latvian and Bulgarian.
Officers from the GLA found some workers had not been paid for three weeks.
Others were charged a £10 administration fee which reduced their pay below the national minimum wage.
A £12 transport charge was made for a three-mile journey and staff were forced to buy their own protective equipment.
Three homes which housed a number of workers were also found to be unfit or unsafe and were closed.
GLA chairman Paul Whitehouse said: "Labour providers who continue to ignore the rights of workers and exploit the vulnerable should be in no doubt that we will catch them through our unannounced raids and other enforcement activities."
The GLA is a government agency which was set up to protect workers from exploitation in agriculture, horticulture, shellfish gathering and food processing and packaging.