Sinn Féin's Mary Lou McDonald has dismissed any suggestion that the Dáil's Public Accounts Committee (PAC) is intent on conducting any sort of 'show trial'.
It comes after the committee last night decided to call in a garda whistleblower in the penalty points issue.
The PAC has agreed to meet Maurice McCabe in private tomorrow to discuss his allegations of misuse of the system.
That is despite the Government suggesting the committee didn't have a role in the matter, and referring it to the Garda Ombudsman Commission.
Depty McDonald today said she is absolutely certain the PAC is acting within its remit.
"It is not the practice, nor has it ever been the intention of the PAC, to conduct what are called show trials," she said.
"That has not happened on our watch - it simply has not happened.
"And those that level that accusation - can I ask them to please produce the instances and the evidence of that? It has not happened".
"It is clearly not our role to make judgments or to make finding against any individual in terms of wrong-doing, we are not a court of law."
However Transport Minister Leo Varadkar today reiterated that there is no need for the PAC to question Mr McCabe because a full investigation will be carried out by the Garda Ombudsman.
Minister Varadkar said he found it "strange" that the internal Garda report into the quashing of penalty points did not interview the whistleblowers in the first place.
"I'm not a policeman but basic detective work is that you talk to the person making the allegation," Minister Varadkar said.
"But that was before Minister Shatter decided to refer the matter to the Garda Siochána Ombudsman Commission (which) was set up to carry out investigations like this.
"And now that that's in play - I think that's the appropriate place."