(DUBLIN) - The Irish government's campaign for a "yes" vote in a crunch EU referendum received a boost Friday, with a new poll showing support growing although many people remain undecided.

Some 35 percent of Irish voters now back the European Union's controversial new Lisbon Treaty, against 18 percent for a "no" vote, according to the Irish Times/TNS mrbi poll.

But 47 percent either do not know how they will vote in the June 12 referendum, or say they will not vote. The last such poll in January gave the pro-treaty camp 24 percent, with 10 percent against and 64 percent undecided.

Ireland is the only one of the EU nations to hold a plebiscite on the treaty -- aimed at preventing decision-making gridlock in the expanding bloc -- and a "no" could scupper it altogether.

The treaty -- replacing the bloc's doomed constitution rejected by French and Dutch voters in 2005 -- was agreed last December amid much fanfare.

A breakdown of polling figures shows that the hardening of the "yes" vote is notably due to a surge of support among members of the ruling Fianna Fail, who are now in favour of the treaty by 47 percent to 10 percent.

But the Times said treaty backers could not be complacent as its first poll during a 2001 referendum campaign for the EU's Nice Treaty gave the "yes" side a bigger lead of 52 percent to 21 percent. The "no" side went on to win a month later.

The rejection of the Nice Treaty -- aimed at EU institutional reform and enlargement -- sent shockwaves through the bloc.

The decision was reversed in another referendum but this time European Commission chief Jose Manuel Barroso has warned that there is no plan B if Ireland votes "no" in the crunch ballot.

New Prime Minister Brian Cowen, who succeeded veteran Bertie Ahern this month, has made the treaty campaign his number one priority and has ordered all levels of his party to launch a general election-style drive to get it passed.

All of Ireland's main political parties support the treaty with only the republican Sinn Fein opposed.

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