There was a 46% increase in the number of unlicensed taxi drivers prosecuted last year.
In 2017, there were 122 prosecutions against fraudulent operators - but this rose to 178 in 2018.
According to details released under Freedom of Information, most offenders didn't have the driver or vehicle licences required.
In total, 236 unlicensed taxi drivers have been prosecuted since the beginning of last year.
Vinny Kearns, a former vice-president of the National Taxi Drivers Union, claims many more illegal taxi drivers are escaping punishment.
He said: "It's good to see an increase in the detections - but I believe it's only the tip of the iceberg.
"If you look at activities over the weekend, I believe that every single weekend in Dublin city there are a substantial number of taxi operating that are neither licensed as the vehicle, or the driver driving it isn't licensed to drive the vehicle."
He added: "There are many taxi drivers drivers who've been driving for years who've never come across an enforcement officer.
"There are only about seven enforcement officers actively out in Dublin - it's just not enough, and they need to bolster those numbers."
