TAXI drivers have threatened industrial action if they are forced to take a test on basic standards in the industry.
Siptu has warned its members would withdraw their services if the Regulator presses ahead with its plans.
The test is already in place for those applying for new licences. But the Regulator wants it to be extended to existing drivers and could introduce this by the end of the year.
Under the exam, cabbies have to prove they understand the laws, are courteous to customers and able to handle emergencies.
They have to answer 90 questions which also cover passenger requirements, vehicle knowledge, maintenance and a "knowledge" exam -- familiarity with their working area.
The exam was introduced for new drivers last May and the taxi Regulator had planned to extend it in 2012 when existing drivers renew their licences. But it is now understood that this could be brought forward to the end of 2010.
The Regulator insisted that all drivers faced having their licence revoked if they did not sit and pass the test, regardless of their experience.
Siptu -- which represents 1,500 drivers in Dublin -- said its members would take to the streets in protest unless the regulator promised to exempt existing licence holders.
"All of the drivers hold a licence by virtue of the fact that they have passed an exam," Siptu's Jerry Brennan said.
"They are now being told they have to pass another exam, and are under threat of losing their licence if they don't pass the test.
"It is very unfair. For instance, the vice president of the Siptu taxi branch, Peter Rogers, has been driving a taxi in Dublin for 44 years.
"I do not accept that he should now have to sit an exam for the licence he has used for 44 years to do his job."
Mr Brennan pointed out that when nursing became a third-level degree course, existing nurses were not asked to sit an exam to prove their capabilities.
"It's quite inevitable we will end up back protesting," he said.
"We will withdraw our service. If there's going to be a protest, it will be in public, unfortunately on the streets."
The Irish Taxi Drivers' Federation, which has 5,000 members in the capital, has suggested a refresher course for existing cabbies as an alternative.
"Bus drivers have to do refresher courses and get a compliance certificate, and this should be sufficient for taxi drivers," ITDF President John Ussher said.