The Labour leader Brendan Howlin says his party won't enter government after the next election simply to make up the numbers.
However, he did not rule out doing business with either Leo Varadkar or Micheál Martin to form the next government.
The Labour annual national conference is taking place today in Mullingar, Co Westmeath.
Members of the party are meeting with a general election on the horizon, as well as the four by-elections looming on November 29th.
Mr Howlin said the party will only enter government again with strict red lines.
He observed: "The party is not a party of protest - it is a party that wants to make a difference in the workers' lives in this country.
"But we certainly won't be there to make up the numbers.
"I have no interest in advising a future conference to participate in any future government unless we radically transform the policy platform of this state."
Labour is launching its by-election campaign at the conference, with candidates running across all four of the constituencies - Cork North Central, Dublin Fingal, Dublin Mid-West and Wexford.
All the party's candidates - John Maher, Duncan Smith, Joanna Tuffy and George Lawlor - are already councillors in their respective areas.
Speaking ahead of the conference, Mr Howlin said their candidates will be 'setting out their stall' this weekend, with the rest of the party discussing Labour's wider policies.
He explained: "We'll be setting out not only our issues for the general election, but also obviously resonating those at local level in the four constituencies that we're contesting.
"I think most of us thought we'd be in a general election by now... but since the Taoiseach decided otherwise we are preparing for four very important by-elections."
He added: "[The by-elections] I think will be a test for the popularity of what I have categorised as a do-nothing Dáil, who have abandoned solving the real challenges of this country - [such as] homelessness, and a dysfunction health service that is not delivering for our people."
Labour says today's conference will focus on five areas - jobs, housing, health, children and climate - with Deputy Howlin to conclude the event with a speech later tonight.