Independent TDs Clare Daly, Maureen O'Sullivan and Mick Wallace 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.
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 gardai 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, Deputies Wallace and Daly attended the non-jury Special Criminal Court for a hearing in which Mr O Coisdealbha, who is learning Russian, was refused bail for a third time.
The TDs are 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 gardai.
Mr O Coisdealbha is charged with membership of an unlawful organisation styling itself the Irish Republican Army, otherwise Oglaigh na hEireann, 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.
The component is a time and power unit, also known as a TPU. It is alleged that the bomb part was in a locker at National University of Ireland, Maynooth, Co Kildare, which was "under the control of Donal O Coisdealbha" under such circumstances as to give rise to a reasonable suspicion that he did not have it in his possession for a lawful purpose on May 13, 2015.
The court heard that 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 give evidence that the refusal of bail is necessary to prevent the commission of a serious offence.
Mr Justice Butler said that the court refused the accused man's application "with great reluctance.
Last night Deputy O'Sullivan defended the trio's decision to stand as independent sureties for the man, saying: "One issue is the amount of time people are spending in jail on remand before being called for trial. 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 and subsequently found innocent but, in the meantime, they have lost their jobs and their livelihoods."
Ms O'Sullivan said that she was "disturbed" by the bail refusal, as the accused was willing to comply with whatever conditions the judge might lay down, adding: "There were three members of parliament there willing to vouch for him and he still didn't get bail."