Newshub can reveal 501 deportees, legal experts and advocates are planning on launching a class action lawsuit, arguing deportees' human rights have been breached.
The 501 deportees are meeting in Auckland on Thursday night to mount the challenge, with the advice of a legal team.
Australian deportee Ace, 28, is being forced to start his life over again. He arrived from Christmas Island Immigration Detention Centre just two weeks ago.
"The last 10 years, all I've known is Australia. I had goals there - that's where my life was gonna be," he told Newshub.
Ace was detained after his prison sentence, while he was trying to get his life back on track. After 15 years in Australia, he leaves a partner, a daughter and an entire life in Brisbane.
"Emotionally it has been difficult - I miss my partner, I miss my kids."
But now thousands of deportees like Ace are pinning their hopes on a new legal challenge. With the help of advocates and legal experts, they're fundraising to launch the class action lawsuit.
"This is the hope that all of us detainees have been looking for. This is the hope we've all been looking forward to."
Law experts involved say they're looking at options in the Australian courts. Any case will focus on inhumane treatment in detention centres and illegal family separations.
They want accountability - and the chance to be allowed back in Australia.
On Thursday night, dozens of deportees are gathering to hear more about it. Prominent human rights lawyer Craig Tuck is involved, as are legal experts in New Zealand and Australia.
"They don't like the way they were treated, they don't like the way they were strong-armed, they don't like the way they were separated from their children," said Tom Harris of Waitematā Community Law Centre.
"And they really don't like the way they're sent back here and haven't been in New Zealand since they were children."
A feeling all too familiar for men like Ace.
"We're not New Zealand's problem, we're Australia's problem. I didn't go to jail in New Zealand, I went to jail in Australia. So maybe if I learnt anything I learnt it in Australia."
The legal challenge is in its early days, but for the more than 2000 deportees sent to New Zealand, it's virtually the only hope they have of being able to go back home.