It has been confirmed by the Taoiseach Enda Kenny that the telephone conversations between some prisoners and their legal representatives were recorded.
He told the Dáil that phone calls between 84 prisoners and legal representatives were "inadvertently recorded".
The Taoiseach also said that prison service knew about this last Wednesday, but the Justice Minister Alan Shatter only found out today.
The revelation only came to light at today's Cabinet meeting and Mr Kenny has now demanded a report on the issue from the prison service.
A bid by Fianna Fáil to have the Attorney General answer questions on the Garda recording controversy in the Seanad has failed after being defeated 21 votes to 19.
Meanwhile, the Taoiseach has suggested that former Garda Commissioner Martin Callinan had a legal obligation to inform the Justice Minister directly of the recording of calls in Garda stations.
Tonight the Dáil begins a debate on a motion of no confidence in Alan Shatter.