236 unlicensed taxi drivers have been prosecuted since the beginning of last year.
There were 178 in 2018 -- up 56 on the previous year.
Details released under Freedom of Information reveal most drivers didn't have the driver or vehicle licences required.
But Vinny Kearns, former vice-president of the National Taxi Drivers Union, claims many more operators are flouting the law.
He wants tougher enforcement.
"There are many taxi drivers who've been driving many years, they've never seen an enforcement officer, because if you look at the average taxi driver, probably carrying out 50 to 60 trips a week, yet never seeing an enforcement officer," he said.
"There are only about seven enforcement officers actively out in Dublin. They need to bolster those numbers," he added.