Pressure is to be put on the British Government to hand over sensitive files gathered during investigations in to the Omagh bombing.
A cross-party group of parliamentarians from Dublin and the UK will debate an emergency motion calling for transcripts of telephone conversations that may involve the bomb suspects to be made available.
The British Irish Inter Parliamentary Body, meeting in Newcastle in the north-east of England, will discuss revelations in a recent BBC TV Panorama programme which claimed telephone calls between the suspects were recorded by the Government Communications Headquarters (GCHQ) on the day of the attack.
The bombing was the worst atrocity during the N Ireland conflict, killing 29 people, including a woman pregnant with twins.
Hundreds more were injured when the Real IRA bombed the Co Tyrone town on a busy Saturday afternoon in August 1998.
Dublin's Fine Gael TD Brian Hayes and the UK's Labour party MP Andrew McKinley, who brought the motion on behalf of 15 cross party members of the body, hope it will put pressure on the British Government to disclose the contents of surveillance gathered more than 10 years ago.
Mr Hayes said the Omagh victims have waited too long for justice.
"It is crucial that all information, documents and transcripts from the surveillance at the time leading up to and after the Omagh bombing be given to the family's legal team," Mr Hayes said.
Although nobody has been convicted for the terrorist attack, families of some of the victims have taken a landmark civil case against five men they believe responsible for the blast.
Named on the family's £14 million lawsuit are Michael McKevitt, the alleged leader of the Real IRA, the man said to be his number two, Liam Campbell, and Colm Murphy, Seamus McKenna and Seamus Daly. All deny any involvement.
