The Labour Party will launch a poster campaign today urging people to back the Lisbon Treaty - while Sinn Féin will officially kick-start its drive to persuade the public to reject it.
Labour leader Eamon Gilmore will be joined by other key party members at Leinster House for the official event.
A few hours before it and across the street in Buswells Hotel, Sinn Féin leader Gerry Adams will unveil his party's campaign for a No vote come June 12.
He will be joined by campaign director Cllr Padraig McLochlainn, Dáil leader Caoimhghín O Caoláin TD, Aengus O Snodaigh TD and MEPs Bairbre de Brun and Mary Lou McDonald.
With just weeks to go to polling day and with Saturday's Irish Times survey showing two-to-one support for a Yes vote, both sides are keen to get their message across before the big day.
Both Fianna Fáil and business body IBEC had called on the public not to be taken in what they said was the No camp's 'scare tactics' and to learn about the treaty from unbiased sources.
Meanwhile, anti-Lisbon campaigner Patricia McKenna from the Green Party said she was considering legal action against the European Commission over what she said was its interference in the Irish political system to secure a Yes vote.
She claimed the majority of their public European meetings had speakers from the Yes camp and virtually nobody from the No side.