Women's Refuge spokeswoman Kiri Hannifin said her organisation had been blindsided by the move.
She said it looked like an attempt to divert attention away from rising police callouts to family violence incidents.
"A cynic would say it's in the Government's interest to have crime statistics going down.
"It's just democracy to have statistics. It's part of the democratic process to have access to these statistics."
Women's Refuge chief executive Heather Henare was set to meet with police at 4pm today over the reporting changes.
Acting police minister Chester Borrows said the changes were necessary to bring New Zealand into line with how family violence was reported in other countries.
"What commentators are failing to account for is that there is no single crime called 'domestic violence', and that the police now include in the category of domestic violence a much wider range of crimes than the previous narrow focus on physical assaults. These changes follow international best practice - they are not hiding the figures, they are about improving Police response to domestic violence."
Mr Bush also moved to quell fears about the new reporting system this afternoon.
He said nothing had changed in the importance police were placing on combatting family violence.
However, the way the information on family violence was recorded was changing to better reflect the relationship between offenders and their victims, he said.
"Statistics around family violence are complex. Our official statistics are the result of counting each offence as it is recorded. There is no offence of "family violence". No one is put before the courts to answer a charge of "family violence"...
"The new reporting system is much more focused on capturing information about the relationship between the offender and the victim."
Mr Bush said family violence could not be reported in 2011 because the statistics were gathered differently would not have been comparable to previous years.
"Our prime focus here is on the real people behind the numbers. An adjustment to how we record information does not affect our ability to understand what is happening with family violence or our ability to gauge the effects our interventions are having."
Mana Party leader Hone Harawira has also hit out at the decision to drop family violence as a reporting category.
He said the move was an attempt to mask an increase in the number of reported domestic violence incidents across New Zealand.
"That will mean in future years the government will declare that domestic violence is coming down. Yet organisations like Women's Refuge know that such statements are bulls**t."
Mr Harawira said there were 78,693 police callouts to domestic violence in 2009.
That went up to 86,710 callouts in 2011 - an increase of 9.25 per cent, he said.
"Domestic violence is going up, not down."
Labour Party spokesman Kris Faafoi said not keeping track of family violence statistics would hobble organisations dedicated to preventing and dealing with the aftermath of domestic abuse.
"If we are serious about tackling domestic violence, then we need these numbers.
"It's our duty to every family to continue to collect and collate them. How else can we determine whether programmes such as 'It's not OK' and 'White Ribbon' are being effective?
"Not collecting this information is not OK."
Mr Faafoi said he feared Government was attempting to "hide the facts" so it could later claim it had cracked down on family violence.
