Revenue's Customs Service has found suspected laundered fuel for sale at two filling stations and at a fuel distributor premises in Co Louth.
The 55,000 litres of fuel have been removed for further examination and investigations remain ongoing.
The two filling stations and fuel distributor premises were searched under warrant as part of an operation on Wednesday.
A spokesperson for Revenue's Customs Service has said the illicit trade of fuels poses a serious threat to the exchequer.
They said: "In addition to the monetary loss, both fuel smuggling and fuel laundering undermine the competitiveness of legitimate businesses, damage the environment, damage consumers' vehicles, and help to sustain organised criminal networks."
The spokesperson also urged businesses or members of the public who have any information regarding illegal activity such as fuel laundering to come forward and report such matters to Revenue in confidence on 1800 295 295.
