Both plants were shut down during early morning raids carried out by officers from Revenue’s Customs Service and armed gardaí.
Revenue said that together, the plants had the capacity to launder about 15 million litres of fuel a year and cause a potential loss to the Exchequer of €8m a year.
The first, a mobile laundry, which was processing fuel when uncovered, was parked at a business premises.
Revenue impounded four lorries, one of which had a concealed tank for transporting fuel, three oil tankers, 28,000 litres of fuel and ancillary equipment.
Three tonnes of toxic waste were also uncovered by officials at the scene.
Revenue said that in a connected search of a private residence and adjoining yard, a slurry tank had been converted into a mobile laundry.
One hundred bags of bleaching earth used to take dye out of fuel and 6,000 litres of fuel were seized along with three cars, two jeeps and one van on the site.
Investigations are still ongoing.