The government needs to take action to encourage people to come forward and report exploitation of migrant workers and how to protect them, Prime Minister Jacinda Ardern says.
On Monday, Samoan national Viliamu Samu, 64, was charged with 18 counts of human trafficking and slavery over a 23-year period in Hawke's Bay.
Ms Ardern told Morning Report she hadn't been briefed on whether complainants in the case would be able to remain in New Zealand.
However, she had asked Immigration Minister Iain Lees-Galloway how the government could encourage people to come forward, she said.
"There are some cases here where there is exploitation occurring where people have the right to work here. So there's a couple of things we need to do here - firstly, weeding out employers who ... might not uphold proper employment practices before they are able to access migrant labour.
"The second thing is making sure we are educating those who may be at risk of exploitation but have legitimate rights to work here.
"The third thing is of course we can provide anonymous ways people that can report on issues around exploitation. We are also undertaking some research into the space of migrant exploitation. We are having a third party do that so that we can have that free and frank exchange with those who have been in this position so we can better understand what's happening and how we can better protect people."
Ms Ardern said she understood Immigration New Zealand (INZ) uncovered the situation relating to Mr Samu while looking into a visa and immigration issue.
"We want to do more to uncover where exploitation is occurring. We had roughly 1800 complaints in the last year. That led to 13 prosecutions, 320 other outcomes and 300 investigations that are still ongoing.
"It is fair to say that there is quite a bit of work in this space but we do need to do more."
Slavery and human trafficking charges
Mr Samu, an orchard worker from Camberly, Hastings who has New Zealand residency, appeared in Hastings District Court on Monday morning following a two-year investigation by INZ and the police.
An INZ spokesperson said the department understands Mr Samu is better known in the community as "Joseph Matamata".
Complainants say Mr Samu closely controlled and monitored their movements, including where they went and who they contacted and he is believed to have promised people well-paid jobs.
Court documents show Mr Samu is charged with using 10 people as slaves between 1994 and 2017. He also faces eight charges of arranging the entry of people from Samoa into New Zealand by deceiving between 2003 and 2017.
He's accused of committing the offences in Samoa and across the Hawke's Bay region.
Each slavery charge carries a maximum penalty of 14 years in prison while the human trafficking charges carry a maximum penalty of 20 years in prison or a $500,000 fine.
Mr Samu was granted bail and will appear in the Napier High Court on 28 January.