Four men have been arrested after around nine million cigarettes with an estimated street value of €4.3m were seized in Co Louth.
The cigarettes had an estimated potential loss to Revenue of €3.7m.
The seizure happened when a truck and a 4x4 vehicle were stopped at a service station on the M1 near Castlebellingham.
The cigarettes are believed to have originated in Malaysia.
Four men, aged 36, 38, 39 and 44, were arrested at the scene.
They are being detained at Drogheda and Dundalk garda stations.
The seizure brings to around 35m the number of cigarettes seized by Revenue this year.