The Government has not conducted a cost-benefit analysis on the financial impact an EU-Canadian trade deal will have on Ireland.
Under the CETA deal, a commercial tribunal will adjudicate - rather than an Irish or EU court - when a company takes legal action against a State.
People Before Profit TD, Richard Boyd-Barrett, described the absence of a cost-benefit analysis on this provision as "incredible".
He told RTÉ's The Week In Politics, that it was "absolutely extraordinary" that such an assessment had not been carried out, adding "we need to ring the alarm bells on it".
Social Democrat co-leader, Catherine Murphy, was also critical of the revelation.
She warned the Government was in danger of signing "a blank cheque" for multi-national companies, by supporting CETA without due diligence.
A campaign group An Claiomh Glas, under the EU's Access to Information on the Environment, requested documentation on a cost-benefit analysis from the Department of Jobs Enterprise and Industry.
A departmental official wrote back this month stating: "I have been unable to locate any records relevant to your request."
The Minister for Education and Skills Richard Bruton, who signed the CETA deal in 2014, said the tribunal would only operate in limited circumstances where there was "blatant discrimination against a company".
Speaking on the same programme, he said that judges would sit on the commercial tribunal.
He added Irish companies who may be discriminated against in the future would no longer would have to take a case to multiple jurisdictions.
A spokeswoman for the Minister for Jobs, Enterprise and Industry said CETA will provisionally apply from April, however it would not be brought before the Dáil for a vote of ratification until a judgement in another trade deal had been handed down by the European Court of Justice.
Under CETA, investment provisions - such as the commercial tribunal - will remain in place for 20 years, even if a future Irish government terminates support for the deal.