Labour leader Eamon Gilmore has accused Sinn Féin of blatantly misleading the electorate over the Lisbon Treaty.
Mr Gilmore made his remarks on a visit to Belfast.
The Labour party, which is calling for a Yes vote on the referendum, took its campaign to Belfast despite the fact that there are not any votes to had in the Northern Ireland.
However Mr Gilmore said his visit, which was hosted by SDLP leader Mark Durkan, was to highlight the fact that a Yes vote will benefit all the people, north and south.
Mr Gilmore also lashed out at Sinn Féin, accusing the party of adopting an entirely politically self-serving approach to the referendum.
He said Sinn Féin was blatantly misleading the electorate in relation to the provisions of the Lisbon Treaty and he said their arguments for a No vote did not stand up.