Seven million contraband cigarettes with an estimated retail value of 3 million euro have been seized by customs officials.
The Benson & Hedges cigarettes were discovered in an articulated truck in Co Louth on Wednesday after a surveillance operation, codenamed Operation Marble.
Follow-up raids were carried out on two private premises in Co Donegal on Friday.
Several people from both Co Donegal and Co Louth were questioned.
The cigarettes, which are believed to be counterfeit, were concealed in a 40ft container which arrived at Dublin Port from China via Rotterdam.
A Revenue spokeswoman said no-one has been charged and that investigations are continuing both nationally and internationally.
So far this year customs officers have seized about 27 million cigarettes with an estimated retail value of 11.5m euro.
The latest find in the container, which was described as containing ceramic tiles on a cargo list, would have lost the exchequer 2.5m euro.