Fianna Fáil TD Éamon Ó Cuív says he has a monumental decision to make in the next 24 hours about whether to leave the party.
The development comes after Deputy Ó Cuív received a letter this weekend from the party whip asking him to refrain from media interviews campaigning for a No vote in the fiscal treaty referendum.
The former minister told RTÉ News that the implication of the letter was quite clear: he would have to leave the party if he did not agree.
He said he would think about its contents over the next day and come to a decision tomorrow. The politician said he faced a stark choice.
It is understood the letter was sent to Mr Ó Cuív at his request following discussions with the party whip on Friday and Saturday.
The letter contained reminders about party policy and a pledge TDs sign with Fianna Fáil promising to adhere to party policy.
Fianna Fáil Whip Seán Ó Fearghaíl confirmed that a letter was sent to Mr Ó Cuív but he said it did not mention potential expulsion.
Mr Ó Cuív resigned as the party's deputy leader in February when he said he could not support the party's position in favour of the fiscal treaty.
