Former deputy leader of Fianna Fail Eamon O Cuiv could be kicked out of the parliamentary party for breaking ranks and campaigning against the European treaty.
Party whip Sean O'Fearghail will meet the Galway West TD this week after he announced plans to push the public for a No vote in the referendum on the fiscal deal - despite Fianna Fail's pro-treaty stance.
"Technically, he could be kicked out of the parliamentary party," said a Fianna Fail insider.
"The whip will meet with Mr O Cuiv and discuss what his objectives are and whether he intends to campaign against the party in the run-up to the referendum."
The decision was taken after leader Micheal Martin reportedly claimed Mr O Cuiv's rogue campaign could not continue.
The former deputy leader told RTE's Raidio na Gaeltachta that he would call on voters to reject the treaty on polling day, May 31.
Mr O Cuiv, who was forced to give up his deputy leadership in February after clashing with Mr Martin over the party's support for the treaty, said he could not do otherwise.
He described the European deal secured by the Government, and supported by Fianna Fail, as very bad for Ireland and insisted he could not campaign for a Yes vote.
The party source said: "If he's going to campaign directly against Fianna Fail, that would have obvious implications for his membership of the parliamentary party.
"One is simply not compatible with the other."