More than €2.2m in additional allowances has been paid to the Office of the President during Michael D Higgins' time in office.
The €317,000 annual payment is separate from the president's salary. It is not audited, and both the Comptroller and Auditor General and the Government said they have no oversight over how the public money is used.
A spokesman for the president's office said the money is mainly used for hospitality and hosting events or to cover costs not met by the president's salary.
Details of the €317,000 allowance emerged during an Oireachtas Public Accounts Committee (PAC) meeting yesterday as members questioned presidential spending.
The cost of the presidency in 2016, including maintaining Aras an Uachtarain, totalled €8.2m, the committee heard.
Secretary General at the Department of An Taoiseach, Martin Fraser, and the Comptroller and Auditor General, Seamus McCarthy, appeared at the meeting to explain what oversight they have over the use of taxpayer funding in the president's office.
Mr Fraser is the accounting officer for Aras an Uachtarain.
Mr McCarthy confirmed the fund is not surrenderable to the State and is not taxable because it is not classed as a salary.
"It is not pensionable, it is not a salary, it's an allowance," he said. "I don't audit that. I audit the issuing of the payment from the central fund of the Exchequer, ensuring the amount that is paid is not in excess of the amount provided for in law.
"The purpose of the allowance is not prescribed in law other than that it is a payment that can be made to the president."
The issue of the allowance was raised by Fianna Fail TD Marc MacSharry. He called for the procedures used to govern the use of the €317,000 to be disclosed and asked for an indication of how much has been spent over the past 20 years.
"What we have established is €317,000 per year is paid to somebody and nobody has oversight of what it is spent on and that is significant," Mr MacSharry said.
A spokesman for Aras an Uachtarain said the allowance is used to meet additional costs not covered elsewhere in presidential funding, such as hospitality costs and state dinners for visiting heads of state.
A president is entitled to a salary of €325,000, but Mr Higgins wrote to the Department of Public Expenditure and Reform shortly after assuming office in 2011, asking that this payment be reduced to €250,000.
Mr McCarthy went on to tell the committee that former president Mary McAleese returned a sum of €357,000 when her two terms ended in 2011.
However, concern was raised that an audit committee tasked with scrutinising spending at Aras an Uachtarain was founded in 2014 but only held its first meetings this year.
Mr Fraser, who sits on the audit committee, conceded this was "sub-optimal" but came about because the committee's chairman was "indisposed".
Other candidates in the upcoming election were surprised to hear of the allowance.
Senator Joan Freeman and businessmen Peter Casey and Sean Gallagher said the fund should be audited.
President Higgins is set to formally launch his re-election campaign today.