Ireland’s parliamentary efforts to ratify the EU-Canada trade deal are unconstitutional, the Irish Supreme Court ruled Friday in the first such legal rejection by an EU member state.

The judgment, broadcast live online, raised divisions within Ireland’s three-party coalition government, which requires support from the environmentalist Green Party to survive.

The case against the government’s ratification of CETA (the Comprehensive Economic and Trade Agreement) was taken by a Green lawmaker, Patrick Costello. He argued that the treaty’s provisions for external arbitration of trade disputes between Canada and EU member states would require an unconstitutional transfer of state authority.

By a 4-3 majority, Ireland’s ultimate arbiter over the country’s 1937 constitution partly agreed with Costello. However, a 6-1 majority found that Ireland’s parliament could proceed to ratify the deal — once the country’s Arbitration Act has been amended to permit such transfers of power.

Deputy Prime Minister Leo Varadkar, who is also Ireland’s trade minister, expressed disappointment with the verdict but said Ireland remains determined to ensure the treaty’s “ratification in full.”

“Our initial assessment is that a referendum is not required and that ratification can follow once some changes are made to domestic law,” said Varadkar, who noted that the treaty had expanded Canadian markets for more than 400 Irish companies.

Costello welcomed his legal win as an “incredible day” that protects “the integrity of our courts system and our constitution” and would further delay, if not permanently block, ratification in Ireland.

Most of the treaty’s rules already have been provisionally applied across the EU, allowing the vast majority of Canadian goods to be imported tariff-free.

Some Irish Greens last year broke with the government’s pro-treaty position, including their own party leaders. The rebels argued that external arbitration of future disputes could force Ireland to accept lower environmental standards observed by Canadian firms in violation of Ireland’s legal commitments to EU climate change goals. Costello’s lawsuit put a halt to government plans to ratify the treaty in parliament last year.