The Irish Congress of Trade Unions Executive Council has voted to back the Lisbon Treaty.
At a meeting in Dublin today, representatives voted by 14 votes to 5 to urge the 600,000 members to vote for the Treaty.
There were eight abstentions.
The leaders of two unions earlier clashed on whether the trade union movement should support the Lisbon Treaty.
Arriving for the meeting, General Secretary of the Civil and Public Service Union Blair Horan said he would be advocating a Yes vote on Lisbon.
He said the fact that the treaty would give legal status to the European Charter of Fundamental Rights would promote social progress and employment as well as combating social exclusion.
Mr Horan said that for 35 years the EU had been the basis of social legislation giving improved employment conditions for Irish workers and he warned that they now need a strong cohesive Europe to combat the worst excesses of globalisation.
He said the treaty could be very important in reversing recent controversial judgments on workers rights by the European Court of Justice.
However, General Secretary of the Technical Electrical and Engineering Union Eamon Devoy, who opposes the treaty, said the court's recent decisions in the Laval, Viking and Ruffert cases had worsened the conditions of workers across the EU.
He said his union had experience of workers being brought in from low-wage economies and being used as subcontractors particularly in construction.
Mr Devoy said the treaty would continue to give precedence to the right of employers to provide services across Europe over the rights of humans.
He cited the situations in Gama, Moneypoint and ESB networks, where the TEEU had found migrant workers being paid as little as $3.81 per hour.
Mr Devoy said that up to now, the union had been able to combat such situations, but he claimed that following the ECJ judgments they would not be able to do so.
Other unions, including Mandate and the Irish Bank Officials Association, were abstaining and Ireland's largest union, SIPTU, will not decide its position until next week.
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