Eighty-seven Stormont MLAs have pledged to vote against any move to remove children's congenital heart surgery from Belfast, it was revealed.
The petition was launched by the Children's Heartbeat Trust, which is lobbying Northern Ireland Health Minister Edwin Poots to preserve the relatively rare service at the Royal Belfast Hospital for Sick Children.
Recently the health authorities recommended operations for youngsters with birth defects should take place in Dublin using enhanced north/south transport links because of the dwindling number of specialist procedures carried out north of the border.
The decision will need to be approved by Stormont Health Minister Mr Poots.
Robin Swann MLA, father of a three-month-old son who is awaiting surgery, said: "Evan William-Robert Swann, born 8th February at 10.32am, who was born with a congenital heart defect, one single wee soul, who has already been through more than any parent would want their child to go through, but he is just that, one soul, a son, a brother, a grandson, a nephew, a cousin, a great-grandson.
"So you can understand the frustration, the anger, the hurt, when commissioners...use flippant lines such as it's a numbers game and this only affects small numbers of children across Northern Ireland."
The change was intended to ensure that doctors carry out enough procedures to keep up their skills, but parents claimed it will put their children at risk.
The Assembly debated the issue today.
Mr Swann added: "Through this motion I want to ensure the minister knows the feeling of every member in this house before he makes the final decision, a decision that is his alone.
"I call on him to make the decision that rejects the recommendation of the (Health and Social Care) Board and accepts the concerns...of the Children's Heartbeat Trust and retain paediatric cardiac surgery in Belfast working in collaboration with Our Lady's Children's Hospital in Dublin."
The board, which commissions services in Northern Ireland, examined options for providing the relatively rare operations, including using hospitals in England as well as Our Lady's Children's Hospital in Crumlin in South Dublin.
Congenital heart disease is the most common birth defect in Northern Ireland, with around 250 babies born with the condition every year, according to the Heartbeat Trust.
Centres must perform a minimum of 400 children's surgical procedures each year to maintain skills, a report said, but Belfast falls short of that number and the volume is decreasing.
The health board's decision followed another review that said, while safe, undertaking heart surgery at the Royal Belfast Hospital for Sick Children was no longer sustainable because of the small population served and lower activity level of medics than recommended by professional organisations.
The board decided children who required planned surgery should travel to Dublin, with an improved transport network from Northern Ireland to help meet the three-hour time-frame for emergency surgery. Support cardiology services in Northern Ireland will be enhanced.