Sinn Fein leader Gerry Adams was absent for one in four Dail sitting days during the first half of the year – one of the worst attendance records of all TDs.
Mr Adams won a seat in the Dail last year after standing down as MP for West Belfast to stand for election in the Republic.
Records show that Mr Adams – who is paid €92,000 a year and claimed €48,000 in expenses last year – has missed 17 of the 68 days on which the Dail sat from January to the end of June.
And 10 of those days were Thursdays – effectively giving the Louth TD a two-day Dail week on a regular basis.
His dismal record is the worst among the opposition party leaders. It is matched by controversial Independent TD Michael Lowry, who also missed one day in four.The only TDs with worse records than Mr Adams and Mr Lowry were Fine Gael Cavan-Monaghan TD Joe O'Reilly, former Fianna Fail minister Willie O'Dea and Fine Gael Cork North West TD Aine Collins.
But all three provided various reasons for their absences, which included family bereavements, illness and official European business.
Sinn Fein last night defended Mr Adams's poor attendance record by suggesting that he was busy travelling widely around the country and working in Northern Ireland.
In contrast, Fianna Fail leader Micheal Martin had a 90pc attendance record from January to the end of June and even Mr Adams's deputy leader, Mary Lou McDonald, had a 91pc attendance record.
Attendance records show that Mr Adams's habit of missing Thursdays developed soon after he first took his seat in the Dail last year.
He missed 22 out of 99 Dail sitting days last year - and 10 of those days were Thursdays.
Ironically, Mr Adams has complained about "our absent friends from the Labour Party" and asked on another occasion why Taoiseach Enda Kenny was "absent" from the Dail.
Mr Adams is able to miss Thursdays in the Dail because Ms McDonald takes over for Leaders' Questions with Tanaiste Eamon Gilmore.
And while the Dail does not meet every Friday, it does have special monthly Friday sittings, of which Mr Adams missed four in six months.
However, Mr Adams is almost always in the Dail on Tuesdays and Wednesdays to take part in the key set pieces of the week - Leaders' Questions with Taoiseach Enda Kenny.
Independent TD Michael Lowry, who missed the same number of days as Mr Adams, defended his record last night.
"As an Independent, I try to balance my time between the Dail and my constituency. I'm able to give proper representation to my constituents and they're very pleased with the level of service that I do give them," he said.
Aside from a few notable exceptions, most TDs have been regular attenders during the first half of this year.
And there were three TDs who turned up for every single Dail sitting in that time - Socialist Party TD Clare Daly and Fine Gael TDs Peter Mathews and Derek Keating.
Mr Keating said it was important for people like Mr Adams to lead by example.
"If it's the case that he is not showing good example, I think that's something Deputy Adams needs to address," he said.
And Fine Gael Meath West TD Ray Butler, who has a 99pc attendance record, said Mr Adams was someone who came down from the North to be a politician in the Dail.
"I'm not trying to belittle Mr Adams but I think that if the rest of us have to be there on certain days, he definitely should be there," he said.
Sinn Fein would not say last night if Mr Adams is actually living in his Louth constituency - or if he returns to his home in Belfast when he is not attending the Dail.
But it said that he was a "hardworking TD" who was effectively representing his Louth constituents.
All TDs are required to "clock in" for work in Leinster House with an electronic key fob at one of several machines provided. Alternatively, they can sign a register.
If they forget to do so, they can ask the Leinster House authorities to correct the record if they can show that they were voting or speaking in the Dail on that day.
Despite Mr Adams's irregular attendance in the Dail, he has still been able to claim €4,795 per month in expenses for the first half of the year. But if he does not clock in for at least 120 days per year, his special travel and accommodation expenses will be cut by 1pc for every day he is short.
His current total is 66 days - which includes 15 days he clocked into Leinster House when the Dail was not sitting.
He will have to turn up for another 54 days before the end of the year to claim his full expenses.