Marc MacSharry has written to the Fianna Fáil party claiming his reputation has been damaged after the Taoiseach failed to give him due process in a complaint made against him.
The Sligo TD said he is "deeply upset and offended" by how he has been treated this week when a motion to have him rejoin the party was pulled from the agenda of a private Fianna Fáil meeting at the last minute.
It is understood the issue arose following an alleged complaint made against Mr MacSharry by a Fianna Fáil councillor in recent days. Mr MacSharry said he is "extremely suspicious of the timing of the complaint" as he said it related to a message sent in a private Whatsapp in July.
He claimed that he had spoken to many people who attended the parliamentary party meeting and "all of them have told me that they assumed that a very serious issue of wrongdoing or grossly inappropriate behaviour had arisen in respect of me".
He added that some assumed that he was the subject of a criminal investigation "such was the cryptic and serious nature" of the explanation given by chief whip Jack Chambers at the meeting.
Addressing the complaint, Mr MacSharry said: "The rules concerning how Fianna Fáil responds to such a complaint cannot change simply because the person who is complained about is not in favour with the party leadership.
"Any person against whom an allegation is made is entitled to due process and the presumption of innocence," he wrote in the letter sent to party headquarters.
He ended by stating that the matter should be dealt with immediately and, irrespective of the progress of the complaint he should be readmitted to the parliamentary party next week.
Speaking in Brussels Micheál Martin said there are “ very good reasons” as to why he couldn't comment about the decision to block Mr MacSharry’s readmittance to the Fianna Fáil parliamentary party.
Government Chief Whip Jack Chambers said he would not be speculating on why he would not allow for MacSharry’s return to the fold on Wednesday night.
Mr Chambers told the Fianna Fáil parliamentary party meeting that he hoped that the issue would be resolved as quickly as possible.
The party is remaining tight-lipped over the circumstances as to why the motion to allow MacSharry’s re-entry was pulled at the last minute.
Mr Martin said: "We are not in a position to comment on it and I’m sorry that we cannot but there’s very good reasons why we cannot comment.
"It is an internal party matter which is being dealt with internally by the party, I’m not at liberty to comment on it any further.”
A motion for Mr MacSharry’s re-admittance after his resignation a year ago had been unopposed at last week’s parliamentary party meeting.
He quit the party last year after the botched handling of Katherine Zappone’s special envoy appointment by Simon Coveney.
Mr MacSharry said that he would not be commenting at this time.
Earlier this month, the Sligo TD told the Irish Examiner he wanted to return to Fianna Fáil as quickly as possible.
A Fianna Fáil spokesperson declined to comment.