Sinn Féin TD Pearse Doherty has said the Seanad in its current form was "an affront to democracy".
Speaking on RTÉ's Morning Ireland, Mr Doherty said the party believed the future of the Seanad should have been referred to the Constitutional Convention.
Sinn Féin has indicated it will now support the Government's attempt to abolish the upper house in the referendum on Friday 4 October.
He said the party was clear in saying the Seanad worked for the interests of the "elite".
Mr Doherty said the party held the long-standing view that it has no valuable role to play in its current form.