Labour leader Eamon Gilmore has cautioned the campaign in favour of the Lisbon treaty against complacency, warning it will be their greatest obstacle.
Unveiling the party's campaign in support of the Lisbon referendum, Mr Gilmore said it would be "challenging", despite the support of political parties and civil organisations, and a close outcome was likely.
"There can be no comfort drawn from the fact that the most recent opinion polls show a clear majority in favour. The polls were giving a very similar message at the same point in advance of the June 2008 referendum, but the result was very different on polling day," he said.
Mr Gilmore said the electorate was in an "angry mood" as a result of issues unrelated to Lisbon. He called on voters to put domestic political issues aside and judge the treaty on its merits.
"In the current climate it is possible that some angry voters, who may have not problems at all with Lisbon, will be tempted to use the referendum to inflict what they would regard as a blow on the government," he said.
"I would urge anyone thinking along these lines to reconsider the position. A second defeat for the Lisbon Treaty will do more damage to the country than it will to Fianna Fáil. Indeed it is the next government that would have to deal with the consequences."
Labour said it was seeking a Yes vote to help restore international confidence in Ireland to secure jobs and businesses, to improve rights of consumers, workers and individuals in Europe and to help Europe function more efficiently and democratically.
The party also supported the treaty in last year's referendum.
"Taken in conjunction with the changes that have been agreed since June 2008 - the commitment that every country will retain the right to nominate a commissioner and the legal guarantees and declarations on issues that emerged as matters of concern in the last referendum - there is now an even stronger case than there was for a yes vote last year," Mr Gilmore said.
"A further no vote would do yet more damage. A strong yes vote on the other hand will show that Ireland is open for business, that we welcome inward investment and the jobs that it brings, and that we are fully engaged and committed members of the EU."
As part of its new campaign for a Yes vote, the Labour Party will conduct an online campaign and has set up a website LabourforEurope.ie to provide information for the public on the provisions of the treaty. Volunteers maintaining the site will answer questions, monitor political sites, use social networking sites and blog. The party is also planning to stream its town hall meetings and other regional events live online, and will post regular video clips on YouTube.
Labour spokesman on Europe and human rights Joe Costello said the party would be treating the upcoming referendum as an election campaign.
""The key to a good election campaign is to mobilise the party members and supporters, and get them knocking on doors, meeting people face to face and asking them directly for their vote. That is what the Labour Party will do for the month of September in every town, city and county in Ireland," he said.
Labour MEP Proinsias De Rossa said the treaty represented a step forward in achieving better protections for public services at European level.
However, Sinn Féin TD Martin Ferris accused Mr Gilmore of a Labour leader of doing a "massive u-turn" on workers rights.
"In December last during a debate on the future of the Lisbon Treaty Gilmore told the Dáil that 'there is a very real concern among working people that the way has been opened for an undermining of the levels of pay and working conditions' and that 'these issues must be satisfactorily addressed before the holding of another referendum'," he said.
"Since then nothing has changed for workers rights in Ireland or across the EU, other than rising unemployment and further deterioration in workers pay and conditions," he said.
Mr Ferris said the declaration on workers rights agreed in June at the Council of Ministers meeting was purely aspirational.
"It will not be added as a protocol to any future EU Treaty, and therefore will have no meaningful legal status," he said. "The concerns regarding workers rights that motivated many people to reject the Lisbon Treaty in 2008 remain in place. Despite this Eamon Gilmore is calling on people to support the Treaty. This is nothing short of a massive u-turn on workers rights."
