Revenue officers seized 664,000 cigarettes worth an estimated €613,000 at Dublin Port earlier today.
The cigarettes were found on a boat that arrived in from Rotterdam.
They would represent a potential loss to the Exchequer of €483,000.
The illegal cigarettes were called 'Marvel' and were hidden in a load of railway sleepers.
A Revenue spokeswoman said investigations into the find are ongoing.
She added: "This seizure is part of Revenue’s ongoing operations targeting the shadow economy and the supply and sale of illegal tobacco products.
"If businesses or members of the public have any information regarding smuggling they can contact Revenue in confidence on free phone number 1800 295 295."
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