A rogue garda who was exposed in the Herald for passing on information to a senior IRA figure is under criminal investigation for the offence.
Justice Minister Frances Fitzgerald has ordered a full investigation into the shock revelations which were disclosed in this newspaper yesterday.
The officer sent information to the dissident figure about two suspected terrorists who had been arrested and were being questioned in a Leinster garda station where the garda was based.
The communication was detected by MI5 who were monitoring the phone of the IRA figure.
This was passed onto the PSNI who in turn informed An Garda Siochana.
In a statement last night the Department of Justice said: "It would be completely unacceptable if information of any kind were to be passed by a member of An Garda Siochana to members of unlawful organisations.
"It is understood that An Garda Siochana is aware from its own intelligence and enquiries of suggestions that a member of the force passed on the names of persons who had been arrested on a particular occasion.
"The member in question has since resigned and is currently under criminal investigation in relation to this and an unrelated matter.
"The Minister has asked the Interim Garda Commissioner Noirin O'Sullivan for a full report on this matter."
The incident happened within the last nine months.
It is understood that the information passed on by the former garda included the names of the detained suspects and how long they were being questioned by detectives.
The garda did not have access to information about what was being said during the questioning of the suspects which took place after their arrest by armed officers under the Offences Against the State Act.
Senior gardai became aware of the situation when they were contacted by the PSNI who had used the British state intelligence agency MI5 to monitor all calls and text messages to and from the IRA man's phone.
The garda later resigned and is the subject of investigations into separate serious offences which may lead to the former officer being jailed.
The garda has very close links to a man that was arrested in relation to the 1998 Omagh bombing in which 29 people were murdered including a woman pregnant with twins.
And in recent times the former garda has been spotted in the company of a middle-aged Continuity IRA member who previously served a lengthy jail sentence for bomb making offences.
Meanwhile, the Herald has learned that a high-profile solicitor has contacted the Taoiseach and Justice Minister about suspected garda collusion in a series of other murders.
John McBurney, who represented the family of murdered Chief Supt Harry Breen at the Smithwick Tribunal, said the Herald revelations are "of major significance".
"I welcome the fact that the Justice Minister is taking this extremely seriously as she should," Mr McBurney said.