Maori are twice as likely to go to jail than Pakeha when convicted of assault, sparking fresh calls from MPs for a Government inquiry into the "biased" criminal justice system.
Ministry of Justice figures reveal in 2015, 26.3 per cent of Maori convicted of assault were imprisoned, compared to less than 13 per cent of Europeans - when both were found guilty of the same crime.
This divide is the largest it has been since figures are available from 1980.
Labour spokesperson for Maori development Kelvin Davis said there's an unconscious bias "right throughout the judicial system".
He said incarceration rates were one small part in the web of the "ugly" criminal justice system that disproportionately affected Maori.
"We just can't keep locking up brown people at twice the rate of non-brown people," Davis said.
"There definitely needs to be an inquiry of sorts as to why Maori are being disproportionately sent off to prison and non-Maori are given fines."
Since data was available from 1980, the highest rate of imprisonment for Europeans convicted of assault - 14.7 per cent - has not eclipsed the lowest imprisonment rate for Maori - 16.3 per cent - in any year.
Green Party co-leader Metiria Turei said unbalanced incarceration rates perpetuated poverty cycles and grew "a culture of distrust" between Maori and the criminal justice system.
She said Maori and Pacific People have fought the "systemic bias" in New Zealand for decades without progress.
"Clearly it's still a serious problem. It's absolutely critical to have a legal system that is genuinely just, because right now it's really clear the legal system does not deliver justice for Maori," Turei said.
Across all ethnic groups, community work was the most common sentence type for people convicted of assault, comprising of 28.9, 31.0 and 30.8 per cent of European, Maori and Pacific cases respectively.
University of Canterbury professor of sociology and criminologist Greg Newbold said judges' sentencing decisions were informed by a number of factors, including prior criminal history, likelihood of reoffending, gang or organised crime connections and employment status.
"If you controlled for all those factors ... I think you would find the courts were not biased against Maori," Dr Newbold said.
"I don't think the courts are racially biased, I think they've got a strong class bias."
He said the Government should conduct research to establish if this issue was a genuine concern.
"The Government should be doing it. The research needs to be done ... They need to find out whether in fact these figures indicate a true bias or a false bias."
Europeans convicted of assault paid a fine, reparation or restitution 13.6 per cent of the time - a more common sentence than imprisonment. In comparison, convicted Maori paid a fine, reparation or restitution less than 6 per cent of the time, less than half the rate of Europeans.
In 2015, 7598 people were convicted of assault -3928 Maori, 2505 Europeans, 894 Pacific People, and 271 other ethnicities.