Gardai issued an on-the-spot fine of €2000 as hundreds of motorists were stopped at a checkpoint in Co Kildare.
Officers were joined by members of Revenue, Customs and the Department of Social Protection as part of an unusual operation.
Customs officers assessed a total of 50 vehicles, and discovered that one was using green diesel.
This led to an on-the-spot fine of €2000 for the driver.
While the Department of Social Protection also spoke to well over 100 people.
Gardai said that these checks were "in line with Department legislation".
Local news site Kildare Now added that PPS numbers were also being checked as part of the operation.
Meanwhile three vehicles were seized for not having tax or insurance, while a total of eight fixed charge penalty notices were issued for "various offences".
A spokesman said last week: "Our Roads Policing Unit Naas were out early this morning performing a multiagency checkpoint with Officers from Revenue, Customs and Excise and Department of Social Protection.
"Customs officers checked 50 vehicles - one road vehicle was being driven with green diesel. On the spot fine of €2000 issued.
"Dept of Social protection interacted with 129 persons in line with Department Legislation.
"Naas Roads Policing Unit seized 3 vehicles for No Road Tax or Insurance - 8 Fcpns for various offences were also issued."
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