Prime Minister Jacinda Ardern says the influx of criminal deportees from Australia to New Zealand - many with no connection to Aotearoa - is a "major irritant" in the trans-Tasman relationship.
Figures released to Newshub under the Official Information Act reveal the number of criminals deported to New Zealand from Australia nearly doubled from 2015 to 2018 after major changes to Australia's migration rules.
In 2014, the scope under which Kiwis could be ejected from across the Tasman was broadened by Australian politicians, leading to an increased number of deportations for what Ardern said was mostly "lower-level offences".
The following year, 261 criminals were deported, increasing to 474 in 2018. Between January 2015 and July 2019, a total of 1806 criminals were deported.
One of the key points of frustration for Ardern has been that many of the deportees have little connection to New Zealand. Figures show 164 of those ejected were 11 years or younger when they last entered Australia from New Zealand.
"The area where we have said it is corrosive is where they are patently deporting people who have no connection to New Zealand," Ardern told The AM Show.
"Every single time I have met an Australian Prime Minister I have raised this issue... They know it is an issue for us, but they are acting within their legal rights, they are legally entitled to do this."
Ardern said the increased number of deportees left a sour taste in her mouth. She said she has "deepened" her language on the issue and on Tuesday didn't hold back in expressing her annoyance.
"If you take it as a relationship that is like family, it is possible to have an irritant whilst actually continuing to maintain a relationship. It is a major irritant," she said.
Nearly a third of the deportees - 595 - also went onto commit crimes in New Zealand. Ardern said that rate of recidivism was less than the general New Zealand criminal reoffending rate.
"I would wager the reason they are a little bit lower for the deportees is the major offences they have committed and have deported for, first, traffic and second, dishonesty charges."
But she also dismissed any suggestion Kiwi authorities don't keep an eye on those who are sent back to New Zealand.
"We actually have the legislative ability to collect all of their identifying, you know, name, address, we can take DNA samples if we need to and we can monitor.
"Individuals are interviewed and then provided services around accommodation. Basically, we know that if you want to reduce recidivism, you don't just plonk someone back in New Zealand."
The data released to Newshub shows the majority of the deportees are male (1690), aged 26-40 years old (912), and Māori (769).
The most common reoffence in New Zealand by the deportees is for "dishonesty" followed by violence and then "drugs and anti-social" behaviour.