Richard Boyd Barrett has called the planned sale of the AIB shares an "affront to democracy"
The Finance Minister says Ireland must pay off some of the national debt with the revenue from the sale of AIB, as a result of a referendum five years ago.
Michael Noonan says the EU's Fiscal Compact - which Irish voters approved in 2012 - means the money raised by the sale has to go towards repaying the national debt.
Minister Noonan was speaking in the Seanad this evening, making his first comments on the announcement that the State will to sell some of the bank's shares next month.
The Government is intending to float around 25% of its stake in AIB. The State currently owns 99.9% of the bank's shares.
It is expected that the upcoming sale will raise around €3bn for the State.
Opposition politicians have said the sale should be delayed until the money could be used elsewhere, with TDs voting in favour of a delay earlier this month.
Michael Noonan, however, says that has never been an option.
He told senators: "The fact is that the fiscal rules are enshrined in Irish law [...] which followed on the referendum where this question was put to the Irish people."
Meanwhile, opposition politicians have continued to criticise the planned sale.
Labour Senator Kevin Humphreys argued: "By insisting on selling it to pay down debt that is already falling, Minister Noonan is throwing away an opportunity to make a meaningful difference to the lives of Irish people."
People Before Profit's Richard Boyd Barrett described the process as a "betrayal of the taxpayer" and an "affront to democracy".
In a statement, he said: “The €20bn that the public pumped into AIB, due to their massive private debts, was driven by a campaign of fear by the establishment, both Irish and EU.
"Now that the bank has finally become profitable the government is going to sell off their share to private interests at a massive loss to the taxpayer [...] It proves this government’s policy is socialism for the rich and capitalism for everyone else."
Sinn Féin leader Gerry Adams earlier told the Taoiseach: “Many people were angry at your mantra that we must 'Keep the Recovery Going'. 'What recovery?', people asked. It is only now that I see what you meant and how you have kept to that commitment.
“The recovery you spoke about wasn’t for working people, the elderly, hospital patients, the homeless, those in mortgage arrears, or our emigrants. No, your recovery was for the bankers.”