Eight people were detained along the Louth border with Northern Ireland on Monday as part of a Gardai operation with the National Immigration Bureau.
The men, all EU nationals, were stopped at Dundalk on Monday morning as they crossed the border in a work van.
It has been reported that they were on their way to pick vegetables in Louth.
The operation saw all south-bound traffic being filtered off the motorway at Dundalk during the day long operation.
The workers, are believed to be seven Romanians and one Lithuanian and had no identification documents.
They were driven to Dundalk Garda station where they were held for several hours.
They were eventually allowed to leave when their employer gave guarantees that documents could be produced.
A Garda spokesman said such operations had been ongoing for several years.
He said that under Irish immigration law, non-Irish nationals are required to carry documentation.
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