The Minister for Justice has described as disturbing a report in the Herald that within the past 12 months a member of An Garda Síochána had texted sensitive information to a paramilitary in Northern Ireland.
Frances Fitzgerald said she is establishing the facts of the situation as a matter of urgency.
The report by Ken Foy in today's Herald claims that a garda, based in a Leinster station, passed sensitive information to a senior paramilitary by text message.
It reportedly involved details about two dissident suspects who were questioned at the station where the officer worked.
A statement from 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 Síochána 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 statement concluded that "the minister has asked the Interim Garda Commissioner Noirín O'Sullivan for a full report on this matter."
According to the Herald report, the paramilitary was based in Northern Ireland and M15 was monitoring his information traffic.
The intelligence agency spotted the garda's text and passed it on to the PSNI, who then shared it with gardaí.
When contacted by RTÉ, a Government spokesperson said Ms Fitzgerald found the report disturbing and is establishing the facts of the situation as a matter of urgency.
John McBurney, a lawyer who was involved in the Smithwick Tribunal into alleged Garda collusion in 1989, said the incident must be thoroughly investigated and the full details made public.