Sinn Féin Senator Máire Devine has been suspended from the party for three months following what the party has described as "unacceptable twitter activity" last night.
Senator Devine retweeted an offensive tweet in relation to Prison Officer Brian Stack who was killed by the IRA.
The victim's son, Austin Stack, said that the tweet was "part of the Provisional movement's campaign to blacken my father's name, firstly they murdered him and now years later they are trying to justify that with these horrendous comments".
Mr Stack said "what is particularly offensive about this is that not only did Senator Devine defame my father but then in a series of tweets she tried to justify her position and accused me of being sensitive".
He added: "There is no place in our democratic institutions for somebody who would support the views expressed in that Tweet and I am calling on Sinn Féin to take immediate action and expel her."
Sinn Féin leader Mary Lou McDonald has said she wants to apologise sincerely to the family of Mr Stack following the post.
Ms McDonald said she had zero tolerance for those whose actions bring grief to victims and their families.
She said Senator Devine understands that she has made a "catastrophic" error of judgement and had been suspended for three months.
Speaking today after making a report to the Sinn Féin Ard Chomhairle, National Chairperson Declan Kearney MLA said: "This is unacceptable behaviour from a Sinn Féin elected representative.
"The Ard Chomhairle has suspended, with immediate effect, Senator Devine from party membership and all party activities for a period of three months.
"The whip has been removed and Senator Devine will be outside of the Leinster House team for that period.
"Sinn Féin strongly disapproves of what has happened. There can be no excuse for the hurt and offence which has been caused to the Stack family."
Senator Devine has apologised for the tweet, saying "It was never my intention to cause any distress or hurt, particularly to victims of the conflict. I want to offer my most sincere apologies to the family of the late Brian Stack.
"I accept the decision by the party national chairperson to suspend my membership of Sinn Féin for three months.
"I deeply regret what has happened, and want to profusely apologise for all the offence and hurt caused by my twitter activity."
Reacting to the news of the three month suspension, Austin Stack said a 12 week suspension is a slap on the knuckles after which the Senator will be welcomed back.
He said the only honourable course of action open to Ms Devine is to resign completely from Seanad Éireann.
He also said Ms McDonald should expel her from Sinn Féin for her "crass, vile and hurtful retweet".
McDonald says Sinn Féin Ard Fheis has been moved to June
Separately, Ms McDonald has said the party's Ard Comhairle has agreed to move its Ard Fheis to June.
It has also backed a motion to go to the Ard Fheis to amend party policy in line with the recommendation of the joint Oireachtas committee regarding terminations of pregnancy for reasons of rape or other sexual assault.
The draft motion supports the joint committee’s findings that it is not possible to legislate for abortion in the case of rape in a compassionate way.
She said the Ard Fheis would happen in good time for Sinn Féin to participate in the legislative process.
She said the efforts of the party now had to be directed in terms of repealing the 8th amendment.
Ms McDonald said all the speculation and analysis around legislation would mean nothing if the 8th is not repealed.
On the issue of 12 weeks she said they had not put that in the motion because they had not seen the legislation.
She said they did not want a party position that says 12 weeks and then if it is 10 or 13 weeks they would have to go back to another Ard Fheis. She said they want to avoid that.
She said the advice and recommendations have to be driven by science and medics.
