Gardaí and Customs officers have seized €14 m worth of tobacco at Drogheda Port.
The haul of 32 million cigarettes and 4,500kg of pipe tobacco is the largest in Europe so far this year, and targeted an organised crime network led by Irish and UK nationals in Europe.
The cigarettes were loaded on a cargo ship in Slovenia and arrived in Drogheda via Lisbon. The Mv Shingle, the cargo ship transporting the haul, was also seized by authorities.
Revenue said follow-up searches are underway both in Ireland and across the continent.
The operation was the result of months-long work with law enforcement agencies in Slovenia and Portugal.
"The illicit cigarette market represents a very serious fraud on the Exchequer as well as undermining health policy and funding organised crime," said Revenue Commissioner Liam Irwin.
"Today’s seizure represents a major blow to those involved in this criminal activity.”.