Immigration New Zealand says illegal sex work is on the rise in New Zealand.
"The noise in the industry and what we're hearing indicate to us that the numbers have gone up and that's concerning because it is very much an underground industry and people can be exploited," Immigration New Zealand assistant compliance general manager Peter Devoy says.
Immigration New Zealand has announced an investigation into the issue as part of a wider focus on exploitation.
The programme's aim is to find out how illegal sex workers are getting into the country, how widespread the issue is and where exploitation is happening and how it can be stopped.
Immigration officers will hear views on the issues from the sex industry, provide education and carry out regulation.
Figures released to 1 NEWS by the Ministry of Business, Innovation and Employment show 179 suspected sex workers were barred from entering the country in the last year to August. Of those, 79 came from Brazil, the biggest group, and a significant number came from Asia.
"On some of the inspection of their goods by New Zealand customs service or looking into their phones it becomes obvious that they are sex workers," Mr Devoy said.
In the past three years, 38 migrant sex workers were sent deportations warning notices, and five were deported.
Voluntary departures, where people cooperate with Immigration New Zealand, were made by 22 people.
"There are migrants from all around the world coming here... different pathways in, they might be coming in as students and supporting themselves by working part-time in the sex industry… there are a number of reasons why," Mr Devoy said.
Prostitution in New Zealand was decriminalised for New Zealanders in 2003, but remains illegal for migrant sex workers.
Mr Devoy said society has changed a lot since then, and evidence from the investigation could lead to fresh discussion over the law on migrant sex work.
Justice Minister Andrew Little said this law is part of the country's obligations to the United Nations "to do everything we can to stop the trafficking of persons".
"It is in part a good measure to prevent the exploitation of foreign sex workers coming to New Zealand," Mr Little said.
Human Rights Commission’s Rebekah Armstrong said while the law was made as a trafficking safeguard, it may be putting migrant sex workers at risk of trafficking and exploitation as migrants feel they cannot report exploitative employers due to the risk of deportation.
Ms Armstrong says The United Nations Committee on the Elimination of Discrimination against Women (CEDAW) has recommended that the illegal status of migrant sex workers should be removed "to reduce its negative impact on women".
A Japanese sex worker living in New Zealand says the fear of deportation is stopping her from working here, but she would if she had no other way to get money.
"It should be legal. I think one of the main concerns people talk about why it's illegal for migrants is people are concerned about human trafficking… but also people who desperately need to work would work anyway and if that’s people working in illegal conditions, it might more likely be unsafe and risky," she told 1 NEWS.
"I think it would be harder to speak up if you're in trouble because even if you got bad clients or been an issue and if you want to report it somewhere… but if you're working illegally it's risking yourself and your right to be here as well."
Some of those involved in the domestic sex industry also want to see migrant sex work decriminalised.
New Zealand Prostitutes Collective co-founder Catherine Healy said she’s heard from illegal workers who have had earnings withheld by brothel operators, and others who have been raped and are too scared to seek support or report incidents to police.
"We think this section (of the Prostitution Reform Act) has actually contributed to creating those conditions that make it very difficult for people to speak out about exploitation," co-founder Dame Catherine Healy said.
Dame Catherine said she was looking forward to seeing the findings of Immigration New Zealand's report.
Mary, a Wellington-based madam, said sex work should be legal for those on work visas, calling it a matter of human rights.
"We have a world-leading model of decriminalisation but sex work is the only occupation that is singled out to be illegal for people with work visas," Mary said.