The annual audit of the Public Representation Allowance (PRA) carried out on behalf of the Houses of the Oireachtas established that five public representatives out of 44 randomly selected for scrutiny had failed to vouch for expenses totalling €5,875.48 over the two years.
The five Oireachtas members required to refund the unvouched expenses were Sinn Féin housing spokesperson, Eoin Ó Broin; Labour education, enterprise and trade spokesperson, Aodhán Ó Ríordáin, former Fine Gael senators John O'Mahony and Gabrielle McFadden and Independent senator Lynn Ruane.
The annual audit of the PRA is carried out to establish if TDs and senators have valid evidence of vouchers, receipts and bills for monies paid to them for expenses.
The audit covers expenditure on expenses under various allowable headings including rent, rates, stationery, office equipment, insurance, cleaning, phone calls, web hosting and leaflet and newsletter distribution.
A random selection of 10pc of Oireachtas members is made every year involving 22 TDs and senators with some politicians being audited in both 2018 and 2019.
The audit found three members had been unable to provide supporting documentation for €3,928.68 out of over €347,000 claimed by those subject to audit in 2019.
It revealed that Mr Ó Broin had been unable to show relevant documentation relating to expenditure of €2,698.08 out of over €21,000 claimed by him in expenses during 2019.
The Dublin Mid-West TD said he had mistakenly included phone bills from a previous year in his expenses for 2019, while also failing to include details of clinics he held on advertisements published in a local newspaper.
Mr Ó Broin said he also did not realise that he could not claim travel expenses for a guest speaker from the UK for a conference he had organised.
"It is my responsibility to know the rules and I fell foul of a number of technicalities," he said.
"I was more than happy to fully reimburse the amount. The audits are an important thing to allow the public to have full confidence that the money is being spent as intended and that the money is reimbursed in full by anyone who knowingly or accidentally spends money outside the rules."
Former senator John O'Mahony claimed €892.88 in expenses that were deemed ineligible out of a total of almost €5,700.
Mr Ó Ríordáin failed to vouch for €337.72 out of approximately €10,700 claim- ed in expenses in 2019.
The Labour Dublin Bay North TD said the claim was made for a print item "in error" as it was included in invoices which were eligible from the same supplier.
The 2018 audit report revealed that former senator and former Longford-Westmeath TD, Gabrielle McFadden, was not able to validate expenditure of €1,831,89 on expenses totalling over €10,000 claimed that year.
Ms Ruane, an Independent senator representing Trinity College Dublin, was found to have had an ineligible expenses claim of €114.91 out of a total of over €10,000.
The report validated expenditure of over €343,000 on expenses by the 22 public representatives subject to audit in 2018.
All parliamentarians who receive vouched amounts are required to hold their own receipts and supporting documents for inspection for a period of five years.
TDs are entitled to a vouched maximum allowance of €20,350 per annum, while the PRA for ministers and junior ministers is €16,000 and €12,225 for senators.