But the agency's acting fraud and compliance manager, Dean Blakemore, said no action had been taken against the 25 brothel owners, including the central Auckland parlour which employed the Chinese chef.
Suspected sex workers on temporary visas are refused entry into New Zealand, deported or asked to leave voluntarily.
"Those who are refused entry are suspected sex workers, but we do not hold statistics specifically on those deported or those who left voluntarily," Mr Blakemore said.
The chef, who is fighting to return to New Zealand, said it was unfair that Immigration was targeting migrant workers but not the employer.
"The parlour owner always gets us to recommend other young Chinese ladies to work there because they know even if he is caught, only the workers will be in trouble," she said.
When approached by the Herald, the parlour manager said it was not her responsibility to check the visas of her workers as the masseuses were not employees but "contractors".
Labour immigration spokeswoman Darien Fenton wants the agency to act against those who broke the law.
"Any employer, including those in the sex industry, who illegally employs a worker should be prosecuted to the full extent of the law," she said.
Carol Wright, a licensed immigration adviser, said Immigration was not doing enough to inform temporary migrants that it was illegal to work in the sex industry.
Visa stamps on passports and Immigration's standard working visa approval letters stated that the holder "may work for any employer in any occupation in New Zealand".
"We would argue ... the statement is extremely misleading and incorrect in that it does not prohibit prostitution," Ms Wright said. Immigration general manager Marie Sullivan said there was not enough space on a visa label to record all of the terms and conditions of the visa.
"It is the responsibility of the visa holder to ensure that they are aware of what they can and cannot do in New Zealand," she said.
"Equally, it is the responsibility of an employer to ensure that every person employed by them is legally entitled to undertake the work."
Ms Sullivan said the agency welcomed information from the public and would investigate where appropriate.
"Immigration officers will determine any brothel operator's liability for prosecution under the Immigration Act if they have failed to take adequate steps to ensure their staff are lawfully entitled to work in the industry."
She added that the act covered not only employer-employee relationships, but also principal-contractor relationships.
Migrant sex workers
Past 12 months
• 25 brothels found employing temporary migrants
• 45* work visa holders refused entry to NZ
• 688* international students deported or faced voluntary departures
• 0 action taken against employers of foreign prostitutes
*Immigration data does not indicate how many had worked in the sex industry
Source: Immigration New Zealand
