Fianna Fáil's Brexit spokesperson, Stephen Donnelly, says the Oireachtas has been "stonewalled" over critical information affecting the island of Ireland.
Mr Donnelly says a leaked Revenue report on the challenges of an open border post Brexit, shows there are elements in Government more interested in "playing party politics" than working to protect the country's economy.
He said: "My colleagues and I have consistently requested, from a variety of government departments, to see reports of this nature, and we have been stonewalled."
Deputy Donnelly says the leaking of the report is hugely disappointing, and the Government's failure to share its contents with business and farming groups is "bizarre and bewildering".
He emphasised that businesses which are heavily reliant on the UK market need Govt support, especially the sharing of pertinent information.
He said: "We have already heard of other government departments being told to stand down and stop any Brexit engagement with their UK counterparts. This needs to be revisited given this report.
"The Revenue Commissioners’ report outlines clearly the task facing Ireland in terms of Brexit, and on the basis of this report, it’s very hard to come to any other conclusion that we are heading for a hard border."
He pointed out that unless something changes, then Irish business and agriculture face a very uncertain future, and called for "significant Brexit initiatives" in next week's Budget.
Mr Donnelly said: "Essentially what the Revenue Commissioners are saying that on current trajectory for the UK, which is leaving the Customs Union and leaving the single market, they can't see any situation in which there is a soft border.
"In other words, there is going to be a hard border.
"That has massive economic implications on both sides of the border. It has huge implications for the agri-foods sector, for tourism, and it has serious implications for the peace process."