Government agencies have been working behind the scenes to prepare for the deportation of criminals from Australia, Prime Minister John Key says.
Mr Key yesterday revealed about 1000 New Zealanders could be in line to be sent home as a result of Australia's tough new immigration policy.
Under new rules introduced late last year, anyone who is not an Australian citizen and has been sentenced to more than a year in prison is liable for deportation.
Labour foreign affairs spokesperson David Shearer said the government had known for some time that a large number of New Zealanders would be affected.
And he questioned why it was only since the issue became public that Mr Key finally started to make noises.
"This will have a very big impact if it's 1000-plus, on New Zealand. I mean these people are going to come back with a criminal history, without their families, without their kids, what about housing, jobs, welfare, everything else that's going to have to accompany those people, that's a very big ask."
Mr Key said the government had known about the situation for a while and he had discussions with Australia's previous prime minister, Tony Abbott, about it as well.
"So we've been aware of the general consequences if all of them are deported to New Zealand.
"People have the right to appeal, and some of those people are winning on appeal in Australia. So in so much that we're just trying to get a sense of how big the issue is for New Zealand, yes of course there will be some government departments that've done some work."
Mr Shearer said many of the people being deported had no family or support in New Zealand.
"The question really is what sort of connections have they got back in New Zealand, now many of them have been away for a long time. Will they be fodder for gangs that are out there, and add to that problem in New Zealand as well?"
The JustSpeak group advocates for change in the criminal justice system.
Its co-chair, Julia Whaipooti, said it was probably a stretch to say people deported back to New Zealand would end up in gangs.
But she said those people who have to complete their prison sentence in New Zealand would be vulnerable.
"Because they have community or whanau to go back to, they have to create their community ... Where are they going to get their community from? From within prison, and it creates a higher chance of reoffending."
Ms Whaipooti said the situation was unusual and government agencies would have to treat each case very carefully.
"We're almost entering uncharted territory with this, because we're not sure who is coming, what connections they have and what kind of offending has been noted."
Mr Key said the government was still working though how it would get information on the people before they arrive via the recently signed memorandum of understanding between the two countries.
He said he would be extremely direct about the issue with Australian Prime Minister Malcolm Turnbull when he met with him in Auckland this weekend.