Finance Minister Paschal Donohoe is to look at an "alternative way" to investigate the controversy around Dara Murphy's Dáil expenses.
Neither the Houses of the Oireachtas nor SIPO have the power to look into complaints relating to former TDs.
"I accept because a number of bodies have now clarified that is not their responsibility, we have to develop an adequate way in which this matter can be dealt with," Mr Donohoe said.
Taoiseach Leo Varadkar has continued to defend the Fine Gael politician who has come under fire for claiming Oireachtas allowances while working as director of elections of the European People's Party (EPP).
Mr Varadkar said it was not in his power to prevent Mr Murphy from taking up the EPP role in 2017, but added that he should pay back his TD expenses if it is found he broke Oireachtas rules.
"I did know he was taking that position as an EPP campaign director and there was no secret about that. I issued a press statement at the time."
After it was suggested that Mr Varakdar could have asked Mr Murphy to resign when he took up the Brussels-based position the Taoiseach said:
I certainly could have but I didn't.
He added: "The record shows that he kept his constituency office open, that he was in the Dáil for 120 days a year, attended votes, but people are disputing that and that's why I think there should be an investigation."
Mr Varadkar previously suggested that the Clerk of the Dáil Peter Finnegan should investigate Mr Murphy's expense claims and Dáil attendances. However, Mr Finnegan has no jurisdiction in the matter.
The Taoiseach said he "can't prescribe" which competent authority carry out the probe but he said: "I think there should be an investigation."