Stand Against Slavery chief executive Peter Mihaere says migrant workers are most at risk of forced labour in New Zealand.

A US report outlining New Zealand's shortcomings in tackling human trafficking show we are "oblivious and ignorant" about forced labour taking place under our noses, an anti-trafficking organisation says.

Enforcement agencies like Immigration New Zealand must be beefed up so they can take more cases against traffickers and ensure prosecutions do not fall through, Stand Against Slavery says.

The US State Department's Trafficking in Persons Report for 2016 placed New Zealand in its top tier for governments who fully meet minimum trafficking standards.

ROBERT KITCHIN/FAIRFAX NZ New Zealand Prostitutes Collective national coordinator Catherine Healy says the legalisation of prostitution has made it easier for sex workers to report suspected cases of exploitation.

However, the report said New Zealand was a "destination country for men and women subjected to forced labour and sex trafficking", while children here were involved in sex trafficking within the country.

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"Some foreign workers are charged excessive recruitment fees, experience unjustified salary deductions, non- or underpayment of wages, excessively long working hours, restrictions on their movement, passport retention, and contract alteration."

While the Government met minimum standards for tackling trafficking, and had increased prosecutions for traffickers, "the punishments imposed were insufficient given the seriousness of the crimes".

Compliance checks had been expanded to ensure work contracts matched those used to apply for work visas and met legal standards, the report said, but the Government "did not consistently identify trafficking victims in vulnerable sectors and continued to treat possible forced labor cases as labor violations".

Last December, two brothers were found not guilty of the main charges in New Zealand's first human trafficking trial.

The report recommending increasing efforts to identify trafficking victims, significantly increasing efforts to catch and punish traffickers, and continuing an anti-trafficking awareness campaign.

MIGRANTS VICTIMS OF FORCED LABOUR

Peter Mihaere, chief executive of anti-trafficking organisation Stand Against Slavery, said forced labour was "prevalent" across New Zealand, particularly in primary industries like horticulture, agriculture and farming.

While some people were trafficked into New Zealand for forced work, Mihaere said most victims were migrants who came here willingly.

"It's people who have either chosen to come to New Zealand and live and then, because they haven't been able to find a job, have found themselves in exploitation situations, or they're students who have come to New Zealand looking for jobs and have found themselves exploited."

'TIME TO WAKE UP'

Government departments did not spend enough time on the issue of trafficking, and enforcement agencies like Immigration New Zealand needed more support.

"They're working very hard, they are under-resourced by a long shot, but they're trying to build up their capacity."

The failure of the first human trafficking trial last year was a sign that more resources were needed, Mihaere said.

"If I was to be tough...there were a lot of things that were not followed through effectively enough so the outcome became what it was, and that was effectively around resourcing."

The Government needed to increase public awareness of trafficking and place it higher on their priority list, he said.

"New Zealanders are oblivious and living in a space of ignorance around this issue and I think it's time they woke up."

FOREIGN SEX WORKERS 'RELUCTANT FOR HELP'

New Zealand Prostitutes' Collective national co-ordinator Catherine Healy said there was a problem with women under 18 becoming sex workers through their social networks of peers, which qualified as trafficking because they were minors.

Healy said there were some foreign women who moved to New Zealand and became sex workers, but were reluctant to receive help as they violated the law that only New Zealand citizens can be sex workers.

"Sometimes they will be in situations where they say, 'Look leave me alone, I don't want anyone to interfere with the fact I'm making money in your country, albeit illegally - I certainly don't want rescuing', and that's not trafficking".

Healy believed New Zealand's decision to legalise prostitution had helped to address sex trafficking, as it allowed those legally working in the industry to call police with their concerns about potential exploitation.

"You have lots of sex workers in New Zealand who are able to say, 'Look I know about a situation', and they're not afraid to speak up."

INSPECTION RESOURCES 'BEEFED UP'

Immigration Minister Michael Woodhouse said he was "pleased but not surprised" that New Zealand had again been placed in the top tier of governments dealing with trafficking.

"We take the sorts of aspects of trafficking that are being described in the report incredibly seriously, and we have taken action to strengthen our laws."

Woodhouse said while the report identified the possibility of forced labour and sex trafficking in New Zealand, it was unclear how significant the issue was.

"I certainly would not be complacent about the possibility that it is more widespread than we think, but at this time I don't see evidence of widespread trafficking in New Zealand."

It was difficult to convince victims of trafficking to speak up, but the Government was working to encourage migrants to step forward and trust authorities.

"The perpetrators of these crimes peddle fear, and therefore it makes it quite difficult for victims to speak up - we're working really hard to change that."

The Government had "beefed up" the resources of the labour inspectorate and immigration compliance teams and encouraged them to work together on trafficking issues, he said.