The Irish Prison Service is investigating how four Sinn Féin TDs had their photograph taken in Castlerea prison with four men convicted of killing a Garda officer.
A picture of Kerry TD Mr Martin Ferris and Dáil colleagues Mr Caoimhghin O'Caolain, Mr Sean Crowe and Mr Aengus O'Snodaigh alongside prisoners Pearse McCauley and Kevin Walsh appeared in the edition of the An Phoblachtnewspaper two weeks ago.
Two other men convicted of the manslaughter of Garda McCabe - Jeremiah Sheehy and Michael O'Neill - are also in the picture along with four other men convicted of IRA offences.
Walsh shot Det Garda Jerry McCabe during an armed robbery on a post office in Adare, Co Limerick, on June 7th 1996. His partner, Det Garda Ben O'Sullivan, was seriously injured when Walsh fired an AK47 on the unmarked Garda vehicle.
A spokesman for the Prison Service said cameras were not allowed in places of detention and that the Sinn Féin TDs who visited the IRA prisoners would have known this. The picture was taken in late August.
"There are no cameras allowed and they were certainly aware of that. An investigation is being held that may well result in disciplinary measures being taken," he said. "They are certainly well aware of the rules."
The spokesman said the area of Castlerea in which the picture was taken is called The Grove and has a lower level of security than other parts of the prison. It consists of a cluster of small houses.
"It is inside the perimeter wall, but it is not a traditional cell block. It's a different type of regime." He said visitors would usually be brought by staff to the area.
Progressive Democrats senator Mr John Minihan called on Sinn Féin to apologise to the family of Gda McCabe "and to the Irish people" for what he said was an "appalling" act of propaganda. "I'm sick and tired of people walking on eggshells around Sinn Féin," he told ireland.com.
"This latest stunt by Sinn Féin is an affront to democracy and is grossly insulting and distressing for the family of the late Jerry McCabe. This garda was gunned down in the line of duty and it is utterly reprehensible that Sinn Féin should seek to associate with and endorse his killers in such an outrageous fashion."
The four IRA prisoners serving sentences for Garda McCabe's killing were originally charged with murdering the detective but they later pleaded guilty to the lesser charge of manslaughter. McAuley and Walsh were given 14-year sentences, Sheehy was jailed for 12 years and O'Neill for 11 years.
The four men have been the subject of an ongoing campaign by Sinn Féin, which wants them released under the terms of the Belfast Agreement. The Government says the four do not qualify for release and they must serve their full sentences.