Immigration New Zealand has been accused of racial profiling.
The agency has admitted collecting data, including ethnicity, to determine how likely an over-stayer is to use hospital resources or commit immigration fraud.
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Those people are then targeted for deportation as soon as possible, but critics say the practice is racist.
New Zealand has 11,000 over-stayers, so Immigration New Zealand is gathering data including ethnicity, type of visa, gender and age, to project who's most likely to be a drain on resources.
"It's racial profiling - it's basically tarring everyone with the same brush," said immigration lawyer Alastair McClymont.
Immigration New Zealand's Alistair Murray told RNZ "it's predicting how someone is most likely to behave based on how their predecessors have behaved."
Once immigrants are singled out as a greater risk, they are deported as soon as possible.
Tongan community leader Melino Maka says it reminds him of the dawn raids on the 1970s, when police would storm the homes of Pacific Islanders who they believed had over-stayed.
"They can say whatever they want to say but racial profile is racial profile, and it's dangerous for New Zealand," he said.
"Is this the revamp of the dawn raids?"
Immigration Minister Iain Lees Galloway says he only heard about the data collection system - known as the harm model - on Thursday morning.
"They use a range of data - if I got any suggestion that they were solely profiling people based on race, that would be unacceptable to me and we would deal with that," he said.
The Human Rights Act states it's unlawful to discriminate based on ethnicity or national origin.
"The advice that I have had so far from Immigration New Zealand suggests that it is not - but I have also asked for additional advice, a full briefing on this pilot program," Mr Lees Galloway said.
The pilot program started 18 months ago, Mr McClymont says, which is when he noticed something had changed.
"I almost fell off my seat when I heard an immigration person confirming what we'd suspected," he said.
"There is massive inconsistency and the only common variable is the race of the applicant."
Mr Lees Galloway says the data isn't being shared internationally, but Mr Maka says it has the whiff of Donald Trump-style immigration policies.