The daughter of a mother and baby home survivor has claimed that 24,000 victims have been excluded from the State's redress scheme.
In February, legislation to establish a redress scheme was approved by the Dáil.
The Bill provides for redress to all mothers and babies who spent more than six months in institutions, and not to those children who were 'boarded out'.
It has been strongly criticised by survivors' groups, who say it unfairly excludes 'up to 40%' of survivors who spent less than half a year in an institution.
In an open letter to Taoiseach Leo Varadkar, Laura Murphy says his claim that its €800million cost 'could otherwise be spent meeting the needs of today or trying to build a better future' revealed 'a lack of understanding of the impact of unresolved past trauma on people's lives today and into the future'.
She says the Government was placing 'the full burden of responsibility on the Irish taxpayer for harm that was perpetrated by Church and State'.
She adds: 'As a result, 40% of survivors are being retraumatised and excluded from the very scheme that was set up to ensure survivor-led restorative recognition and reparation.'
Ms Murphy first appealed to then-taoiseach Micheál Martin two years ago to retract the part of the State apology that blamed society for the mother and baby home atrocities.
She now wants all survivors to receive redress and for the scheme to ensure the Church contributes and is brought into a 'meaningful process of truth, reconciliation and reparation'.
In her letter to the Taoiseach, Ms Murphy writes: 'Considering the irrefutable evidence of the abuses committed by the Catholic Church and the profits made from human trafficking, forced unpaid labour, illegal adoptions, illegal vaccine trials and stipends from the State... it is outrageous that they are absolved of their responsibility to give back what they took from the Irish people. Instead, the full burden of responsibility is being placed on the Irish taxpayer.'
Kathy Scott, cultural archivist and founder of The Trailblazery, is backing Ms Murphy to raise awareness of the effects of unresolved trauma. Ms Scott said: 'This is a huge moment of reckoning for Ireland and provides an opportunity for us to be one of the first countries to take a stance and do the right thing for our citizens past, present and future.'
She added: 'Just as trauma is a cyclical process, so too are the perpetual rounds of inquiries, commissions and reports that have cost the Irish taxpayer an estimated €1.5billion over the past 22 years.'