Fianna Fáil leader Micheál Martin has said a Commission of Investigation would be the only proper way to deal with allegations of garda inaction or incompetence between 2007 and 2009.
He said he found it difficult to accept that an internal review of correspondence relating to claims made by garda whistleblowers within the Department of Justice was a credible response.
Speaking on RTÉ's Drivetime, Mr Martin said the information he provided to Taoiseach Enda Kenny was sufficient to move towards a Commission of Investigation.
That information relates to ten cases involving alleged garda inaction or incompetence on claims of assault, endangerment, abductions and other matters.
Mr Martin said the response to the ten cases and to the penalty points issue was lacking.
He said he believed the issues were not dealt with properly when the complaints were initially made.
He also said Minister for Justice Alan Shatter should apologise to garda whistleblower Sergeant Maurice McCable after it was claimed that he had not co-operated with an investigation into the penalty points issue.
He said Mr Shatter did not explain to the Dáil about the conversation held with Sgt McCabe by the Garda Confidential Recipient, Oliver Connolly, who was sacked this week, and should now make a comprehensive statement to the House.
Both Mr Kenny and Tánaiste Eamon Gilmore have expressed confidence in Mr Shatter who has directed his Department to conduct an internal review of correspondence relating to claims made by garda whistleblowers.
They include a claim by Sgt McCabe that serious crimes were not investigated properly by gardaí
Correspondence obtained by RTÉ News shows that Sgt Maurice McCabe sent an email to the Department of Justice on 12 December 2012.
In the email he said that last February it was "relayed back to me through the confidential recipient that there was no evidence to the matters which are now in the media".
He added it was "reported back to me that there was a comprehensive investigation carried out...and there was also no evidence, despite otherwise, to the following: very serious incidents never investigated, serious incidents not investigated properly...".
A reply from the Department of Justice, dated 17 December 2012 states that of the 12 individual allegations made in the report to the Confidential Recipient, it is advised that "11 had already been thoroughly investigated...and that no evidence of corruption or malpractice had been discovered".
This evening the Department issued a statement saying "Minister Shatter has initiated a review of all correspondence between his Department and Garda Whistleblower Sergeant Maurice McCabe.
"That review is ongoing".
Earlier today, Mr Kenny played down calls for an independent inquiry into the ongoing allegations relating to a garda whistleblower.
He said Mr Shatter was entitled to conduct an internal review of communications in his department and that legislation would now be amended to enable whistleblowers to go directly to the Garda Síochána Ombudsman Commission.
The Tánaiste also said he has confidence in Minister Shatter, saying he does a good job, is hard working and is very thorough.
Finance Minister Michael Noonan added his support for Mr Shatter this afternoon, saying that it was "obvious" that opposition parties were trying to smear him.
The internal review of correspondence relating to claims made by a whistleblower that serious crimes were not investigated properly by gardaí is continuing at the Department of Justice.
According to an alleged transcript of conversation between Sgt McCabe and Mr Connolly, the allegations had been raised with Mr Connolly in early 2012.
Based on the alleged transcript, it was claimed in the Dáil yesterday that the minister knew about the allegations two years ago.
It is understood that Sgt McCabe first emailed the department in December 2012 about the general issue and received a reply a few days later.
Independent TD Clare Daly has said Mr Shatter must account for the fact that he was in possession of very serious allegations for at least 18 months and stood over a situation where nothing was done.
Speaking on RTÉ's News At One, she said she has seen correspondence from December 2012 between the minister and the whistleblower saying that the complaints had been looked into and that they did not stand up.
Rabbitte says Shatter may have been 'mistaken'
Earlier, Minister for Communications Pat Rabbitte said Mr Shatter may have been mistaken when he said Sgt McCabe did not cooperate with the inquiry into the penalty points controversy.
Mr Rabbitte said that quite clearly if Minister Shatter had said this in the Dáil, then he was under that impression.
Speaking on RTÉ's Today with Sean O'Rourke, he said Mr Shatter was not a minister who would mislead the Dáil.
He said it may have been a simple mistake, and if there is, it should be corrected.
Mr Rabbitte said he had confidence in Minister Shatter, adding that he was a reforming, hard-working and insightful minister.
He said he would not rule out the possibility of a Commission of Inquiry being set up under the Commissions of Inquiry Act to investigate the situation.
However, he said he would not "jump in straight away".
Mr Rabbitte said there would be a report from Minister Shatter at Tuesday's Cabinet meeting.
Elsewhere, Labour Senator John Kelly has urged Mr Shatter to quickly deal with the latest allegations.
He said if he cannot do this then the minister should resign.
Senator Kelly said the issues raised by Sgt McCabe had been fudged for far too long.
Meanwhile, Minister Shatter has defended his decision to sack Mr Connolly.
In a statement, Mr Shatter said that Mr Connolly's position became untenable after a transcript of a confidential conversation between Mr Connolly and Sgt McCabe was made public.
Mr Shatter said it is his intention to abolish the office of the confidential recipient and to enable the Garda Síochána Ombudsman Commission to receive and investigate whistleblower allegations.
