Independent TDs Mick Wallace, Clare Daly and Maureen O'Sullivan offered to stand bail at a cost of €5,000 each for a man accused of IRA membership and being in possession of a component part of a controlled explosive device.
University graduate Donal O'Coisdealbha (24) of Abbeyfield, Killester, Dublin 15, was one of several men arrested last May on foot of an investigation by the Special Detective Unit (SDU) into the activities of the IRA.
Senior gardaí have told the Special Criminal Court their inquiries uncovered "advanced plans" by the IRA to mount bomb attacks during the visit to Ireland of Britain's Prince Charles.
Yesterday, Mr Wallace and Ms Daly attended the non-jury Special Criminal Court for a hearing in which Mr O'Cosidealbha, who is learning Russian, was refused bail for a third time.
The TDs were among a group of seven people who planned to stand as independent sureties in the event the young engineering graduate was granted bail pending his trial, which may not take place until 2017.
Mr Wallace and Ms Daly, who both recently spent a brief time in jail after they refused to pay court fines arising from security breaches at Shannon Airport, attended court for the bail application, which was robustly opposed by senior gardaí.
Mr O'Coisdealbha is charged with membership of an unlawful organisation styling itself the Irish Republican Army, otherwise Oglaigh na hÉireann, otherwise the IRA, within the State on May 13, 2015.
He is also charged with possession of a component part of an improvised explosive device - namely a time and power unit also known as a TPU - at a personal storage locker under his name at Protector Life Sciences at the National University of Ireland in Maynooth on May 13, 2015 under such circumstances as to give rise to a reasonable suspicion that he had not got it in his possession for a lawful purpose.
The court heard the accused man has applied for bail on four previous occasions, twice at the Special Criminal Court and twice at the High Court.
The State objected to Mr O'Coisdealbha's bail application. Detective Inspector Anthony Lenehan, of the Special Detective Unit, told the three-judge, non-jury court that there was an objection to bail on grounds of the "seriousness of the charge".
Detective Chief Superintendent John McMahon told the court there was an objection to bail under Section 2 of the Bail Act. The section allows a Chief Superintendent to give evidence that the refusal of bail is necessary to prevent the commission of a serious offence.
Mr Justice Butler said the court refused the accused man's application "with great reluctance".
Mr Wallace and Ms Daly did not reply to attempts to contact them last night.
However, Ms O'Sullivan defended the trio's decision to stand as independent sureties for Mr O'Coisdealbha.
"There are a couple of issues with this, one of which is the amount of time people are spending in jail on remand before being called for trial," she said. "It can be three years, if not more, that people spend in Portlaoise (jail) waiting to go on trial.
"We have met people who have been two and three years on remand in jail and subsequently found innocent but in the meantime - they have lost their jobs and their livelihoods."
Ms O'Sullivan said she was "disturbed" by the bail refusal as the accused was willing to comply with whatever conditions the judge might lay down.
"He's 24 years old, finished school and has been working in Maynooth University, although that job is gone now," she said.
"I'm not taking away from anything he may or may not have done. But there were three members of parliament there willing to vouch for him and he still didn't get bail."