The arrest - on suspicion of supplying workers to a salad processing packhouse without a valid licence - was made following an investigation also involving the UK Border Agency, Kent and Essex police and Gravesham Borough Council.
A number of farms, business premises and residential addresses were visited and agency officers detained 20 individuals for suspected immigration offences.
Investigations are continuing into suspected serious exploitation of workers, including the examination of the accommodation provided.
During the arrest, £4,000 found was identified as representing unpaid wages for January and February. The GLA is in the process of ensuring that this money is paid to the workers. The man was bailed until 27 July.
GLA chairman Paul Whitehouse said: "This was an excellent example of inter-agency cooperation. We shall continue to work to ensure the fair treatment of workers and a level playing field for businesses. We shall also work to identify any evidence of forced labour that may lead to further charges."
He added: "Unlicensed activity can often be used to shield serious exploitation of workers from the authorities. We will not stand by and see the unscrupulous activity of gangmasters put low-paid workers at risk of going into debt or debt bondage."