The fares on the cross-Border Enterprise rail service between Dublin and Belfast will increase from next Monday.
On the service, which is operated by Translink in the North in co-operation with Iarnród Éireann, a single Dublin-Belfast ticket will rise from €31 to €34, a day return will increase from €32 to €35 and the monthly return on the route will rise from €46 to €48.
The rise follows increases in a range of InterCity promotional fares in the State by Iarnród Éireann, introduced this week.
Discounts on these fares will be reduced and include discounted tickets such as five-day return, family fares, InterCity commuter season tickets and contract tickets, as well as day and monthly return saver fares.
A spokeswoman for Iarnród Éireann said the effect on fares was increases of between 4.5 per cent and 7 per cent, with most fares increasing by under 6 per cent.
However, the chief executive of the Consumers' Association of Ireland, Mr Dermott Jewell, said the increases were far above inflation. He said the timing of increasing discounted fares at the beginning of summer was extremely poor and would particularly affect families.
Iarnród Éireann's comment that most fares were increasing by under 6 per cent was a classic look-at-the-basket response, he added.
In fact, the Belfast-Dublin route, with an increase of about €3, was a 10 to 11 per cent increase. Probably a domestic consumer would only travel on the route occasionally, but for the business consumer, the increase was significant, he said.
The Iarnród Éireann spokeswoman said the marked-down promotional fares had been very heavily discounted in the first place.
"The fares revision is necessary as Iarnród Éireann is faced with increasing inflationary pressures while undertaking the largest ever Irish railways investment programme," she said.
Fuel and insurance costs alone had increased dramatically in recent years, she said. Fuel (oil and electricity) costs increased from €10.9 million in 2000 to €17.7 million last year, an increase of over 62 per cent. Insurance costs had risen by more than 300 per cent in three years, from€1.158 in 2000 to a forecast €4.431 m in 2003.
A Translink spokeswoman said the service was affected by the annual increase in rail operating costs, an increase which was standard across the industry.