The Supreme Court has struck down the EU’s Comprehensive Economic and Trade Agreement with Canada.
CETA was negotiated between 2009 and 2016 and has been in provisional operation since 2017.
The deal removes 99% of tariffs on goods and EU officials predicted it would generate an extra €10.9bn worth of trade.
Opponents of the deal say it weakens environmental protections and hands too much power to large corporations through the establishment of Investment Courts.
Green party TD Patrick Costello challenged the agreement on constitutional grounds and said he is pleased the seven-judge Supreme Court has ruled in his favour.
“This challenge was about a legal question,” he told Newstalk.
“How do we ratify CETA? What is the legal way to do that? The question of should we ratify CETA is a separate political question and that’s the question that needs to be answered now.
“I will be working with the broad coalition that is opposed to CETA, that is opposed to investor courts and sees them as dangerous.”
The Court concluded that ratification was possible if the Government amended the 2010 Arbitration Act and Taoiseach Michéal Martin said that a referendum was unlikely to be needed.
“CETA has been very beneficial for increasing trade for Irish companies - which benefits our economy, which creates additional wealth for the country and creates additional jobs,” he said.
“I’m very strongly pro-free trade because we’re a small economy, we’re very open and we’re global and we export most of what we produce.”
A number of Green TDs have said they are opposed to CETA and Mr Costello said he “looked forward” to campaigning in a referendum against the trade deal.
When asked about the rift in the coalition ranks, An Taoiseach said, “like many issues across Government, we will work through this.”
Main image: Jean-Claude Juncker, Justin Trudeau and Donald Tusk attend the signing ceremony of the Comprehensive Economic and Trade Agreement (CETA), October 30, 2016. Picture by: REUTERS/Francois Lenoir