People Before Profit and Solidarity have launched their candidates for the upcoming European Parliament elections.
TD Richard Boyd Barrett said the two parties were "cautiously optimistic' that their four candidates could make "a big impact" in the campaign.
He said the candidates were activists of a "new generation" who would seek to "radically change Irish society, and Europe as a whole".
He argued that the EU needed to change as it had become "too corporate - excluding working class people".
People Before Profit has three candidates: Gillian Brien in Dublin; Adrienne Wallace in Ireland South; and Cyril Brennan in Midlands North West.
Solidarity has a single candidate, Rita Harrold, in Dublin.
Asked why they fielded two candidates in Dublin, rather than a unity figure, Mr Boyd Barrett said: "Elections are an opportunity to argue for radical change - we are not narrowly electorate.
"This is our biggest ever intervention in the European Parliament elections."
