Presidential candidate Liadh Ní Riada has sent a letter to Michael D Higgins asking him to explain his use of public money.
The Sinn Féin MEP says the incumbent has serious questions to answer before the final debate of the campaign tomorrow night.
She says Michael D Higgins has to explain his use of the government jet to fly to places in Ireland at the taxpayers' expense.
She also says he needs to explain media reports that the Office of Public Works has spent significant money on Mr Higgins' private home in Galway.
Taking to Twitter today, Ms Ní Riada said: "It is my strong view that discussing these issues publicly is the only means left to reassure our citizens that public finances are being properly used, particularly at a time of huge difficulties for many families.
"These are very legitimate questions, which should be answered in advance of tomorrow night's debate so that we can move on and talk about the next seven years for our country."