A black market fuel laundering plant has been shut down near the border.
Customs officers and armed gardai swooped on the operation near Castlebayney, Co Monaghan, on Thursday morning and seized two tankers, 20,000 litres of laundered fuel and 140 bags of material used to bleach the diesel.
The Revenue said cash, bank drafts and cheques worth 60,000 euro were also recovered.
The operation was based on intelligence, officials said. Follow-up raids in Cavan and Monaghan recovered 14,000 litres of laundered diesel from a filling station with the fuel also being used by two haulage firms.
Revenue earlier this year said criminals running black market fuel operations had been "effectively eliminated" with the crackdown estimated to have saved about 200 million euro in 2014.
And customs chiefs urged anyone with information on similar operations to contact the authorities.
"Revenue would like to remind anyone tempted to buy cheap mineral oil from an irregular source of supply that there is a high possibility that they are buying laundered or smuggled fuel," it said.