Revenue has seized more than 3.3 million cigarettes at Rosslare Europort in Co. Wexford.
Officers stopped a Polish registered truck which came on a ferry from France and found the cigarettes within its load.
They have a retail value of €2.4million, which is a potential loss to the exchequer of over €1.8 million.
A man in his forties is being questioned as part of the investigation.