Revenue officers say they seized almost 6.5 million smuggled cigarettes at Dublin Port yesterday evening.
The cigarettes are said to have arrived here from Vietnam, via Rotterdam.
They were found in a shipping container - which was searched with a mobile x-ray scanner - said to contain 'paper'.
The seized cigarettes - described as 'cheap whites' branded “Jin Ling” - have a retail value of €3.5 million.
In a statement, Revenue said its officers simultaneously carried out searches in Roscommon and Waterford.
The investigation is said to be ongoing, with a view to prosecution.
"This latest seizure brings to almost 15 million the number of smuggled cigarettes that Revenue have seized, entering the country in containerised cargo, in the last two weeks," the statement adds.