Minister for Transport Leo Varadkar has said there is no justification for additional funding for the railways.
Speaking on RTÉ's News At One, Mr Varadkar said the public was not getting good value for money from Ireland's railways at the moment.
He said Irish Rail was getting 50% of all money that the Government puts into public transport, for operating costs alone, but Irish Rail only carried 15% of passenger journeys.
Mr Varadkar said the Government wanted to maintain all existing rail services and make some improvements if it could, but it could only do that if it reduced the cost base and increased the numbers of people using the railways.
He rejected suggestions that there were plans to close railway lines, but when asked if closures were something he might have to countenance in the short term if the budget could not be balanced, he said he could not pretend otherwise.
Mr Varadkar said if there was extra money it would make more sense to put it into Bus Éireann, Dublin Bus and other road transport that could carry more people more efficiently.
He said: "If you believe in public transport and you want fast, efficient and affordable public transport, at the moment, the best way to do that is to put more money into the buses.
"The failure of Irish Rail to deliver the savings to date really underlines that and makes the situation much worse for them."
He added that the payroll savings planned at Irish Rail were well over a year behind, and he hoped the Labour Court would make a decision in the next few weeks which workers could then ballot on.
SIPTU, meanwhile, has criticised Mr Varadkar’s comments indicating that funding may be withdrawn from Irish Rail and directed into other transport companies.
SIPTU organiser Paul Cullen said: "The minister has on a number of occasions made clear his preference for forms of transport other than rail.
"In reality the cost base of rail transport in Ireland has risen because of additional expenditure on infrastructure and compliance with a number of new regulatory frameworks which have been imposed in recent years."
He added: "If the minister follows through with his threat to reduce funding this will result in a cash crisis in Irish Rail and lines will have to be closed.
"His comments come a week before the Labour Court will adjudicate on cost containment proposals proposed by the company and will only harden the attitude of staff in Irish Rail who have given everything since 2008 with nothing in return."