The Court of Appeal is considering a major change to the way cases of international child abduction are dealt with.
The Hague Convention for international child abduction is used when a parent takes a child from their place of usual residence to another country, without the permission of the other parent.
The treaty was originally designed to protect mothers who sought the return of their children when their partners kidnapped the children.
But in the years since the treaty was created, data shows the majority of cases involve a mother fleeing a domestic violence situation, not just in New Zealand but across the globe.
For that reason, the Court of Appeal is considering whether one of the clauses in the treaty which would prevent the return of a child should have wider scope.
That is the issue of a grave risk that the child could be thrust into an intolerable situation.
As the law is read at the moment, if a mother is the victim of domestic violence but there is no evidence the child will be harmed, then the child returns to its father.
Lawyers Ben Keith and Daniel Vincent are arguing that if the mother is at risk of serious harm, so too is the child.
"We did say when we sought leave that we were not seeking to revisit the Family Court judges finding in relation to the child," Keith said in court on Friday.
"What we do say is that the child's circumstances include at least the mother's trauma."
Mum suffers years of domestic violence in Australia
Keith was arguing on behalf of Jane, a battered mother RNZ talked to in December 2018.
She had been the victim of years of domestic violence at the hands of her former partner, and she fled Australia after an assault in July 2017.
She said she only fled with her child because she could not get support in Australia, because she is a New Zealand citizen.
The lawyer for the father, John Gwilliam, said there is support for the mother in Australia, when quizzed by Justice David Goddard about her living conditions if she were to move back.
"We know that there are social agencies who can step in the breach immediately, in terms of social housing and so forth," Gwilliam said.
Goddard replied, saying: "But does that show that the situation will be tolerable, or that there will be some Bandaids on an intolerable situation to prevent it from being catastrophic, rather than intolerable?"
Gwilliam said the mother would have support from her parents, who live in New Zealand.
And while he admitted there would be little support from the father or his parents, he said it is unfathomable she would not have support.
"At the end of the day the court must come to assessing the grave risk to the child.
"I would have to accept there is a risk, but I would submit a fairly negligible risk given the realities of family support that's available.
"I cannot see the maternal grandparents allowing their grandchild to be in that situation."
No risk to mum if parents live apart, lawyer argues
As for domestic violence, Gwilliam admitted that a child living in that scenario would be untenable.
But because the parents would be living apart, he said the risk is gone.
The judges also asked about the social support on offer if Jane were to return to Australia.
Goddard said it was obvious there would not be much support, and the president of the Court of Appeal, Justice Stephen Kós, agreed.
"You can't really go out on a bowling night with a state agency," Kós said.
"It's not the sort of thing they do."
Summing up at the end of the day, Kós said the court's decision would be significant.
"We're going to be required obviously to consider a case, the A decision which is almost a quarter century old and give that some reconsideration," he said.
"The case has been very well argued and the fact that principal parties are here represented as a result of the grant of legal aid, shows the importance of legal aid, not just to the parties here but also to the body of the law because this case will affect dozens of cases beyond the immediate one."
Justice Kós reserved the decision.