Police are having to abandon some prosecutions because of a lack of funding - not only for police but for the whole justice sector, the Criminal Bar Association says.
New figures show that in 2013, police started an average of 260 new investigations of family violence every day but fewer than 40 percent of them were recorded as offences.
Figures from the Family Violence Clearinghouse show 95,080 family violence investigations were launched in 2013 but, of those investigations, only 37,880 were recorded as offences.
Criminal Bar Association president Tony Bouchier said on Tuesday that police could not afford to prosecute as much as previously.
"I think it's purely to do with money. It's not only the police but it's the whole justice sector that is being starved of money and as result is not performing."
The report also found that between 2007 and 2013, 56 percent of the 176 female homicide victims were killed by a family member.
Clearinghouse research fellow Pauline Gulliver said the figures showed family violence remained an important issue affecting a significant number of New Zealanders.
She attributed a rise in police safety orders with being behind the drop in family violence investigations leading to a prosecution.
"It comes down to us to ask the question whether or not they're being used appropriately - 'can we be sure of the safety of the person who has received a police safety order'? Police safety orders are only a temporary measure."
A police safety order puts temporary restrictions on a person officers believe is a threat, and may be involved in a domestic violence incident.
It is the second release of family violence data in a fortnight, following the report by the Violence Death Review committee in June.
Kiri Hannifin from the National Collective of Women's Refuges said she was worried about the difference in numbers of investigations and recorded offences.
"I'm really surprised that the police attend so many events, or investigations as they call them, but yet there are so few offences.
"I think that there's a real pressure [within the police] to keep crime stats down. But as a domestic violence worker, actually I want to see domestic violence stats go up, because that's the only way we're going to get accountability and safety."
Labour claim police charging fewer people
Labour Party justice spokesperson Andrew Little told Radio New Zealand's Morning Report programme on Tuesday he had been told on good authority that police were charging fewer people across a range of offences in order to meet the Government's crime targets.
"Well I would certainly suggest the police were required to be independent of the government of the day. If they are motivated to do anything on the grounds that their political masters are telling them they have targets to meet, that would be a major problem."
However, the police acting assistant commissioner - prevention, Dave Trappitt, dismissed the suggestion there was pressure to keep crime statistics down.
"No, I don't believe that's the case. There's certainly no pressure on our staff to record matters as an occurrence as opposed to an offence. There's no such instructions or directions given to our staff in that area at all."
Police Minister Anne Tolley said Mr Little's comments were unfounded and outrageous, and Labour's continued attacks on police showed how desperate the opposition was to get a headline in election year. She said she was assured that police prosecuted where appropriate.
The Clearinghouse data showed that between 2005 and 2013, the number of sexual offences against adults reported to police increased from 1187 to 1848.
The number of reported sexual offences against children increased from 1278 to 2071 in the same period.
Dave Trappitt said it was possible one contributing factor was an increased confidence by victims who came forward to report sexual assault.
"I think there is less tolerance in the community. They're far more prepared to report family violence, and we would encourage that."
Several family violence initiatives were launched by government last week to combat family violence.
They included proposals to appoint a special adviser on victims' rights, introduce GPS monitoring to keep victims safe, and amend the legal process when defendants declined to give evidence.
Justice Minister Judith Collins said the Government was looking at ways to help get a conviction when women were too frightened to give evidence.
"That's one of the reasons I'm also very much looking at whether or not an alleged offender who does not give evidence in his own offence, whether or not a jury will be able to draw a negative inference. I think that that will be something which will be hugely helpful to victims of family violence."
However, Kiri Hannifin from the National Collective of Women's Refuges said they did not deal with systemic problems such as policing, approach and whether or not the threshold to convict was too high.
"None of those things have been dealt with in those initiatives. It's only piecemeal, incoherent, bits and bobs: fine, but not going to make a difference."