Ireland's powerful farming lobby pledged on Tuesday to back the European Union reform treaty in a June 12 referendum, giving the government and pro-treaty parties a boost after opinion polls showed the "No" camp gaining ground.

The Irish Farmers Association (IFA) agreed to back the treaty designed to streamline the way the EU is run after Prime Minister Brian Cowen said he was ready to veto any world trade deal that undermined Ireland's agricultural interests.

"It is a unanimous agreement of the (IFA executive) council that we are prepared to support a 'Yes' vote and we will be writing to all our members to explain the situation to them," IFA president Padraig Walshe told reporters in Dublin.

Ireland is the only country holding a referendum on a treaty which replaces the EU constitution rejected by French and Dutch voters in 2005, meaning one of Europe's smallest countries could sink the project designed to end years of diplomatic wrangling.

An opinion poll late last month showed the "No" camp was closing in on supporters of the treaty, who include Ireland's three biggest political parties.

Ireland's agriculture industry only accounts for about 2 percent of gross national product (GNP) but some of Ireland's best known companies are food groups and the IFA remains highly influential in rural areas where many people's livelihoods still depend on farming.

Thousands of Irish farmers, who fear EU trade proposals would lead to a flood of cheap imports such as foreign beef, took to the streets of Dublin to protest during a visit by European Commission President Joes Manuel Barroso in April.

The IFA had said all along that it had no problem with the treaty itself but threatened to join a loose coalition of groups opposed to it if their concerns over a proposed, but unrelated, World Trade Organisation (WTO) deal were not addressed.

Cowen, who earlier met the IFA, said in a statement he had reiterated his view that current EU plans for a WTO deal were unacceptable.

But crucially for the IFA, which had wanted a tougher stance, Cowen used the word veto three times in his statement.

"The Taoiseach (prime minister) assured the IFA that he was prepared to use the veto if a deal that is unacceptable to Ireland is put to a vote," Cowen's office said.

Cowen later told reporters, however, that there had been no fundamental shift in his stance.

"If I can be of assistance and clarify anything ... I've always been available to do so," he said.