A married couple, who are both serving as TDs, have admitted they were both claiming overnight allowances of €140 on the double for almost three years.
Fine Gael's Joe McHugh and Olwyn Enright said they had decided last July to stop making two claims on the €140 nightly expense, which is available unvouched to all government deputies.
The couple, who have been married since July 2005, had been double-claiming the expense for three years, even though they would presumably have been sharing the same accommodation the vast majority of the time.
A conservative estimate put the cost of the double claim at €30,000 over the course of their marriage before a decision was made last summer that they would only take a single allowance.
The Fine Gael press office said that the two TDs had only ever claimed expenses that they were "entitled to".
A spokesman said: "Last summer, Olwyn and Joe decided that even though both of them were entitled to claim the subsistence allowance, only one would do so.
"For the period since July, only one subsistence allowance has been claimed."
Donegal TD Joe McHugh, who was a senator at the time the couple married, said: "The situation has changed and we have a statement from the press office that is available regarding this.
"We have had a number of queries about this and it wouldn't be accurate to say there was double-claiming – the hypothesis is simply not accurate." The Donegal TD called for more transparency in a system where the vast majority of expenses claims do not have to be vouched.
Each member of the Dáil or Seanad is automatically entitled to travel and overnight allowances. If they live within 15 miles of Leinster House, they get a flat daily allowance of around €60. Those living further away can claim the flat allowance or an overnight allowance worth €140 along with generous mileage claims.
The double claiming of expenses has already proven controversial this year with Beverley Cooper-Flynn continuing to accept a €40,000 Independent TD allowance even after rejoining Fianna Fáil. Cooper-Flynn eventually agreed to stop claiming the allowance.
The €40,000 allowance is made available to Independent TDs to assist them in the absence of a party-political structure for support.
Fine Gael's Liam Twomey was also doing the same and had claimed almost €100,000 in extra allowances after being elected as an Independent TD.
Immediately after joining with Fine Gael, he had offered up the annual payment but was told it could not be accepted for "legal reasons". Twomey agreed with Fine Gael leader Enda Kenny that it would instead be used "to develop the party and my political base in Wexford".
Government sources said close scrutiny of the 166 TDs and 60 senators and their overnight and mileage allowances would yield other supposed "abuses".
One TD said: "The reality is that many politicians would have access to an apartment or the home of a relative or friend whilst in Dublin. The problem lies in the fact that these are all unvouched. The overnight allowance should only be paid on production of a receipt from the hotel in which they stayed or on production of a mortgage showing the money has been used to buy a second property in Dublin."