Authority chairman Sir David Carruthers noted the possibility of differential treatment on the basis of ethnicity.
"Pre-charge warnings are more likely to be given to non-Maori offenders than to Maori offenders.
"Statistics show that a much higher proportion of Maori offenders committing eligible offences have previous criminal convictions.
"While the authority has not come across evidence that clearly demonstrates differential treatment on the basis of ethnicity is happening, the possibility that it could happen is enough to reinforce the need for more guidance on the exercise of police discretion in this area."
Other findings included:
• It is unclear whether victims must be consulted before a pre-charge warning is given and whether the warnings should be used when the victim is seeking reparation. Warnings don't usually require reparations.
• There is a lack of clarity about the extent to which warnings should be given to offenders with criminal and police histories. In some cases, warnings are given to offenders with "substantial" criminal histories.
The report was sparked by a complaint to the IPCA by an officer whose daughter had her car broken into in the Bay of Plenty last year.
A pre-charge warning was used, and the officer felt a "blanket approach" was being taken, which undermined victims' rights.
"The authority's investigation into the officer's specific complaint identified a number of issues with pre-charge warning policy and practice. As a result, the authority undertook a wider review."
New Zealand Police deputy chief of Maori, Superintendent Wallace Haumaha, said police had recently began a review of the warnings process.
"The IPCA's findings supports this programme of work and police are confident we are addressing each of the concerns raised."
That work will involved addressing the "inconsistencies" in using the warning system, he said.
"However, as the IPCA have acknowledged, there is no evidence to suggest any differential treatment is being given on the basis of ethnicity."
"Police do reiterate the findings of the IPCA that they found no evidence that differential treatment was being given on the basis of ethnicity."
When asked to clarify that statement, Haumaha said:
"The IPCA found while the [pre-charge warning] process was being applied universally - and noting previous offences are not a barrier to a [warning] - offenders were less likely to be eligible if they had an extensive or serious offending history.
"We must also be clear that [warnings] are only one way to respond to offending behaviour before a prosecution is needed.
"Therefore, the current programme of work aims to provide staff with more guidance on the options available in the preventative space that applies to everyone."
Haumaha said more consideration would be given to victim's wishes in regards to reparation.
"Victims of crime remain at the heart of what we do and I am confident this ongoing programme of work will continue to reaffirm this commitment."
New training will be given to staff to meet these goals, he said.
Regular audits of the process will also be conducted.
