Waterford's Green Party TD says he would be in favour of re-establishing the railway between Waterford and Rosslare.
It comes as the All Island Strategic Rail Review is proposing re-instating this line, along with a number of others around the country.
However, it's understood this would mean the scrapping of plans for an extension of the Greenway from Waterford to Wexford.
Deputy Marc Ó Cathasaigh says while the existing Waterford Greenway has been a success, it's not the right choice for every old rail line.
"The Greenway has been transformative for the likes of Dungarvan and Kilmacthomas. I don't think that's necessarily the right fit for every piece of rail," he said.
Marc Ó Cathasaigh TD
Deputy O'Cathasaigh points out that the existing Waterford Greenway was well past the point where a rail line could have been re-established.
"The line was very far away from rehabilitation," he says.
"It would have required massive investment to bring it back as a rail route - with questionable return."
He says issues such as population density must be taken into account.
"Heavy rail relies on having good population density to provide a good service," he says.
He highlighted the potential of the Waterford to Rosslare line, saying: "It's still in pretty good shape, not as far away from being brought back into use as many of the other lines that have been converted into Greenways."
He added: "We talk about it as Waterford to Rosslare, but we actually should be talking about the full corridor that links Rosslare all the way across to Limerick and indeed onto Foynes Port."
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