Meanwhile, leaders from the two parties continue to have war of words
A new online tool has calculated that Fianna Fail and Sinn Fein are more compatible with each other than with any other party.
The Smartvote.ie tool, says their policies agree in 2 out of 3 cases - despite their intense rivalry.
Only 50% of Fine Gael and Labour policies are in agreement.
It comes as Gerry Adams claims Fianna Fáil TDs are "offended" by their party leader - who says Sinn Fein is a "mafioso" organisation.
He's hit out at the comments from Micheal Martin in the latest war of words between the two opposition parties.
Yesterday the Fianna Fáil leader said Sinn Féin operated under "a vow of omerta" to stifle internal dissent.
Deputy Adams - and his Sinn Fein colleague Caoimhghin Ó Caoláin - both claim Fianna Fáil members find that offensive:
Yesterday, when asked if he felt that Sinn Féin may take from Fianna Fáil's supporters, Mr Martin said: "In terms of they stealing our Republican cloak - they have not. [...] They're not a Republican party in the true sense of the word - they run themselves like a mafia organisation".