Members of the opposition are demanding clarity from the Taoiseach over his decision to contact planners in Clare County Council following a phone call from Donald Trump.
Speaking in Washington DC yesterday during a lunch event on Capitol Hill, Mr Varadkar recounted a story from when he was tourism minister.
Mr Varadkar said he got a call from Mr Trump, asking about proposals to build a wind farm near Doonbeg, where Mr Trump owns a golf resort.
The Taoiseach said: "I rang the county council and inquired about the planning permission - and subsequently the planning permission was declined - thus the landscape being preserved.
"And the president has very kindly given me credit for that - although I do think it probably would have been refused anyway."
Leo Varadkar says he has talked before about the matter, and that ministers often make enquiries about planning matters.
He had previously made a reference to the incident in a Time magazine interview last summer.
Clare County Council, meanwhile, says no formal objection was logged from any public representative in relation to the wind turbines.
— Clare County Council (@ClareCoCo) March 15, 2018
However, the Labour leader Brendan Howlin says Leo Varadkar is guilty of a serious lapse of judgement.
He argued: "The Taoiseach should recognise that, apologise for his original interference, and say that on reflection it was entirely inappropriate for a Cabinet minister to interfere in a planning matter, as he apparently did."
Fianna Fáil's Michéal Martin also called for greater clarity.
Taoiseach needs to be more transparent in relation to his intervention with Clare County Council on behalf of President Trump regarding a planning application for a wind farm . Who did he ring? What was the nature of the intervention?
— Micheál Martin (@MichealMartinTD) March 15, 2018
Solidarity TD Paul Murphy suggested the Taoiseach's comments raise 'very serious questions'.
Deputy Murphy asked: "Who did he phone in Clare County Council? What did he say? Why does Clare County Council say they have no record of this phone call? Varadkar and Clare County Council must provide clear answers."
A spokesperson for the Taoiseach yesterday said: “It is normal for Ministers to seek information on planning applications when issues are raised by citizens, businesses or investors.”
He said the matter “has been mentioned publicly on many occasions by the Taoiseach” adding that it “was not a court case or judicial matter.”