The revelations mean that many court cases - ongoing and historic - could be challenged by defence teams.
Judges have been warned of disruption to ongoing criminal cases after it came to light earlier in the week that telephone recordings were made at many Garda stations from the 1980s until last year.
One case before the Special Criminal Court in the Republic, involving two men charged with IRA membership, has already been adjourned as a result of the controversy.
Last year, an eight-year tribunal led by Judge Smithwick, concluded that there had been Garda collusion in the IRA murders of senior RUC officers Harry Breen and Bob Buchanan in 1989, who were ambushed as they returned from a meeting at Dundalk Garda station.
On Thursday Taoiseach Enda Kenny warned that state inquiries such as this one could have been compromised by the latest scandal in the An Garda Siochána.
"I don't know the scale of the actual contents of what are in all those tapes but we're concerned about it," he said.
"It's a serious issue, where in some cases court cases have been dealt with, others reaching up as far as tribunals, it may have implications for some of the findings there."
A lawyer for the Breen family has suggested Judge Smithwick can reopen the investigation if he thinks he has been misled or attempt being made to pervert the course of justice.
Solicitor John McBurney said: "Judge Smithwick must be troubled. I think he will be genuinely shocked."
Mr McBurney said there could be evidence in the tapes on not only the Breen and Buchanan murders, but other major cross-border cases.
The tapes, their existence should all have been identified, the transcripts should have been prepared, I believe they are now being prepared and they will be essential documents in many different cases.
John McBurney, Breen family solicitor
Meanwhile, at a Stormont Justice Committee, chairman Paul Girvan raised concerns that the tribunal was unable to access Garda phone records in the investigation.
"It seems highly irregular that when lawyers in the Smithwick Tribunal sought phone records from Dundalk Garda station, none were forthcoming. However, we are now discovering that for 30 years Garda phone calls were being monitored and recorded," the DUP MLA said.
"There are a series of important questions as to why this information does not seem to have been disclosed to the tribunal. It is now paramount that the Irish Government hands over these tapes for an independent forensic examination of information relating to the Smithwick Tribunal."
Ulster Unionist Justice spokesperson Tom Elliott MLA echoed the need to investigate whether recordings could have assisted the tribunal.
He said: "The question must be asked of Alan Shatter, the Republic's Justice Minister, just how many tapes are in existence of calls between Dundalk Garda Station and other stations in Drogheda, Monaghan and Dublin, which might hold information which would have assisted Judge Smithwick in his deliberations?
"It may well be that the full story of the Smithwick Inquiry has yet to be told."
Irish Justice Minister Alan Shatter has denied knowing about the practice until he was briefed on Monday evening.
Raymond McCartney, Sinn Féin vice-chair of the Justice Committee, questioned if the RUC or PSNI had any similar recording system in place at any time.
He said: "The concerns obviously are about the human rights abuse that this practice represents but the question that must be answered by the Justice Minister and the Chief Constable is - was there a similar practice in operation here?
"I intend to raise these issues with the Minister through the Justice Committee and my party colleagues on the Policing Board will similarly raise them with the Chief Constable."