A group has been setting up a blood bank using directed donor blood in the wake of a court ruling that a baby could receive "vaccinated" blood during open-heart surgery.
But anyone using the would-be rival to NZ Blood Service "wouldn't be complying with legislation".
The rival group, called "Liveblood", said it was "working tirelessly" to let New Zealanders access the "safest, freshest, best directed donor blood" in moments of surgery or emergency.
It also stated in the longer term it was working on having sperm and bone marrow donations and creating a "whole parallel health system that keeps you in control of the choices made about your body".
It comes after the High Court ruled doctors could make medical decisions for a baby at the centre of a case about blood from donors vaccinated for Covid-19.
The 6-month-old needed open-heart surgery, which was performed on Friday, but his parents said they had donors - who had not been vaccinated for Covid - lined up.
They said they were concerned about the possible health impacts of their child receiving blood from vaccinated donors.
Otago University immunologist associate professor James Ussher previously said if any remnants of Pfizer vaccine made it into donated blood, it would be very short-lived.
It posed "no safety concerns", he said.
In New Zealand, the NZ Blood Service has sole right to collect and store blood for transfusions, Dr Jim Faed, senior lecturer, haematologist and transfusion medicine specialist, University of Otago, said.
"No one else has the right - it has to be produced by NZ Blood Service, he said.
Faed warned if Liveblood did try and use donated blood for transfusions they would be "exposed to legal risks".
"The issues with just collecting blood is that it needs to be screened properly and thoroughly for any issues.
"There's so much control that goes on behind the scenes that wouldn't be able to be replicated and if someone tried to they wouldn't be complying with legislation."
Faed said he doubted any hospital, public or private, would accept blood from any other source than the NZ Blood Foundation.
One of the biggest worries would be that there could be a mistake made during the screening which could prove fatal to someone who was already frail or vulnerable.
"The NZ Blood Service has a beautifully crafted process for keeping people safe. Think carefully about what you're doing," Faed said.
*This story first appeared on Stuff's website.