LABOUR TD Joanna Tuffy has warned that other members will join her in campaigning to save the Seanad in defiance of the party line.
Tanaiste Eamon Gilmore has said Labour will run a strong campaign to abolish the Seanad, but Ms Tuffy turned up at the launch of the Democracy Matters campaign to save it.
"I'll be canvassing because this is about the nature of our democracy. In the Labour Party, we've always accommodated that," she said.
The Dublin Mid West TD said other Labour members shared her view, and she expected them to join the No campaign as well.
A party spokesman said it was "relaxed" about Ms Tuffy's stance and had no difficulty with members taking different views.
Ms Tuffy was among the diverse band of supporters who turned up at the Democracy Matters campaign launch in Dublin's Smock Alley Theatre.
They included former Progressive Democrats leader Michael McDowell, former Fianna Fail minister Mary O'Rourke, former Green Party senator Dan Boyle and Bertie Ahern's former speechwriter Brian Murphy.
Also there was Dublin businesswoman Glenna Lynch, who questioned Sean Gallagher's business record during the RTE 'Frontline' presidential debate in 2011.
Fine Gael's former legal adviser Dr Brian Hunt was present, but said he had never been a member of Fine Gael. He said he had drafted the group's Seanad reform bill, which would allow for senators to be elected by the public rather than councillors at the next general election due in 2016.
"The Seanad is broken, so let's fix it," he said.
Democracy Matters has challenged Taoiseach Enda Kenny to a public debate during the campaign. However, it will select Senator Katherine Zappone – ironically nominated to the Seanad by Mr Kenny – for the proposed head-to-head rather than Mr McDowell.
A Fine Gael spokesman said Mr Kenny would be "fully involved" in the campaign, but declined to say if he would take part in a public debate.
Democracy Matters estimates it will have a budget of around €60,000. Fine Gael and Labour are expected to spend €250,000 on their campaigns.
Independent senator Feargal Quinn said he had been in the Seanad for 20 years and believed the electorate could be persuaded to save it.