Those who use the M50 motorway occasionally face paying tolls 50pc higher than the normal charge, when barrier-free tolling is introduced next year.
And drivers who refuse to pay toll fees face fines of at least €40 -- and the possibility of being brought to court.
The National Roads Authority (NRA) yesterday revealed that, from August, motorists who use a pre-paid electronic tag on the M50 will pay €2 per trip.
Those who set up a number plate-based payment account will pay €2.50. But car owners who do not have a tag, or do not have an account, will be hit with a €3 toll.
The move has been slammed by consumer groups which said it was "unfair" and "anti-consumer". They said that, unless the system was changed, people would avoid using the upgraded motorway.
The charges were outlined at a public hearing into the tolling system yesterday. The NRA has had six objections to its proposals to remove barriers and replace them with electronic tolling.
The move is certain to affect thousands of holidaymakers from outside the capital who make their way to Dublin Airport via the motorway every summer.
Hauliers without an account will also be hit with increased charges of up to €6.10 per journey, while concerns have been raised on whether cars from outside the state could be tolled.
National Consumer Agency chairwoman Ann Fitzgerald said it made "no economic sense" for occasional users to purchase an electronic tag.
"It forces you to get a tag," she said. "This is the first time that barrier-free tolling has been used and it's going to be rolled-out across the country so it has to be fair," she said.
"There's a tag with hidden charges. If you're an occasional user it makes no sense. It's a question of doing it in a fair way."
Consumers Association of Ireland chief Dermott Jewell said there should be no difference in the tolls paid. The measure was "inequitable, unfair and anti-consumer", he said.
Some 90,000 motorists a day use the M50 and earlier this year the Government paid a reported €600m to buy back the road from National Toll Roads, which operated the Westlink toll bridge.
The NRA admitted that when barrier-free tolling was introduced next August, some motorists from outside Ireland would escape paying the charge.
Not until a pan-European database of vehicle registrations was available could it guarantee that all vehicles would pay the toll, a spokesman said.
The AA described the proposed system as a "monster in the making", saying it would be overly complex and costly. It would cost €25m a year to run, and a two cent per litre "infrastructure levy" on fuel should be introduced instead of a toll.
"What the NRA is proposing for the M50 is insanely complex and enormously expensive," AA public affairs manager Conor Faughnan said, labelling it, "an expensive and complex mechanism for collecting a tax".
He added of the €80m collected in revenue each year, over 30pc would disappear in costs, which was "scandalously wasteful".
But the NRA defended the new system, saying that tags would allow motorists to use any tolled road in the country. Incentive schemes were common in countries which used barrier-free tolling, as using an electronic tag resulted in lower administration costs.
On the increased charges for hauliers, a spokesman said that truckers paid lower tolls on the Westlink toll bridge because the cost of the trip was subsidised by the taxpayer. The improved motorway would result in speedier journey times, leading to savings.