Almost 700 drivers caught illegally using Belfast's bus lanes have had their fines scrapped - because they are not from Northern Ireland.
Dozens of penalty notices are written off every week as the offender cannot be traced.
In two cases, the same motorist was clocked 17 times by cameras - but wasn't fined a single penny.
The database used to trace registered vehicle keepers - operated by the DVLA (Driver & Vehicle Licensing Agency) - stores details of vehicle owners based in the UK only.
It means drivers from the Republic of Ireland, mainland Europe and beyond can drive without fear of punishment in the city's bus lanes - while tens of thousands of fines are issued to local people.
South Belfast MLA Christopher Stalford said: "I think it's further evidence that the practical consequences of these bus lanes just haven't been thought through.
"I think they need to be looked at again.
"It is not right that Northern Ireland citizens, particularly ratepayers in Belfast, should be penalised for driving around the city while people from outside of Northern Ireland can break the law with impunity."
The Department of Infrastructure said 691 penalty charge notices had been "generated but not issued" because of lack of drivers' details between June 2015 and September this year.
The figures were obtained after a Freedom of Information request from the Belfast Telegraph.
Two cars were each caught illegally driving in bus lanes on 17 separate occasions, while a third was spotted 15 times.
Yet none of the three were fined a single penny - because they could not be traced. It will infuriate the thousands of Northern Ireland motorists who have been hit with fines of up to £90 a time.
Last month this newspaper revealed how the cameras had raised more than £2.7m in their first 15 months - even though they had been expected to generate just £500,000 every year.
Up to August 31 this year, a total of 51,811 penalty charge notices were issued. They were worth a combined £2,729,021 - or £6,245 a day on average.
One camera, at Donegall Square East beside City Hall, was responsible for 17,972 penalties totalling £975,242.
The other hotspots are Castle Street, where drivers have been issued with 14,184 fines worth £706,366, and Great Victoria Street, where 8,167 fines worth £442,978 have been generated.
The wave of negative headlines around Belfast's bus lanes has led to warnings that shoppers are being deterred from visiting the city.
Glyn Roberts from the Northern Ireland Independent Retail Trade Association said a review is needed. "We do need to see an open and honest review of how these bus lanes are enforced," he stated.
"A good starting point would be a yellow card system, where people are given a warning first, which we have put forward to the Department for Infrastructure for consideration.
"It does make for a lot of negative headlines at a time when we should be focusing on the good things that Belfast has to offer this Christmas," Mr Roberts added.
A spokesperson for the Department for Infrastructure said: "A Penalty Charge Notice (PCN) is issued to drivers who contravene bus lane regulations, in line with legislation. The department would prefer that drivers adhere to the law, meaning fewer PCNs would be necessary.
"The department can only issue these to registered vehicle keepers based on address details provided by the DVLA.
"When the vehicle keeper addresses are not available, then it is not possible to formally issue a PCN, which eventually results in some being written off.
"However, PCNs continue to be recorded for that particular vehicle even though the earlier ones have been written-off."