Immigration New Zealand (INZ) has admitted to targeting particular nationality groups in individual investigations, including those involving sex workers.
Massey University sociologist Paul Spoonley said all deported sex workers appeared to be Asian, while those being stopped from entering NZ for intending to do sex work are mainly Brazilians.
The 27 sex workers deported in the last three years, either voluntarily or by force, were foreign nationals from China, Hong Kong, Taiwan, Malaysia, India, Macau and Thailand.
"It echoes an earlier concern that the Immigration Minister moved quickly to change," said Professor Paul Spoonley, an immigration expert.
"It would be interesting to know whether INZ does prioritise or profile sex workers and their nationality."
Immigration Minister Iain Lees-Galloway suspended a programme in April which involved racial profiling of overstayers by INZ to prioritise deportation.
At the time, an INZ official said the agency used "country of origin" as one of several factors to profile and then prioritise the deportation of overstayers and others who have breached their visa conditions.
However, the agency denied there were any official orders to target certain ethnic or nationality groups in its sex worker investigations.
INZ announced last week that it was taking a proactive approach to better understanding issues within the sex industry as part of its wider work on exploitation.
"Given its limited resources, how does INZ prioritise in a way that is equitable?" Spoonley asked.
Under the Prostitution Reform Act 2003, only New Zealand citizens and residents can legally work in the sex industry.
INZ assistant general manager Peter Devoy said people who are risks to public safety, or who are engaged in criminality or posed a risk to the integrity of the immigration system were prioritised for deportation.
"Absolutely under no circumstances would INZ ever deport people based on single factors and the ethnicity of a person is never a deportation consideration," Devoy said.
"There are no directions for targeting specific nationalities, but individual investigations include particular nationality groups."
Devoy said Section 392 of the Immigration Act 2009, which identified the relationship between the Immigration and Human Rights Act noted that immigration decisions would also be discriminatory.
"This section notes that immigration decision-making is inherently discriminatory as it involves different treatment of individuals based on personal characteristics," Devoy added.
Devoy said INZ would, under the new programme, be ensuring employers, facilitators of service and sex workers that they understood their rights and obligations.
"As with other industries, there will continue to be regulatory activity in this industry," he added.
One sex worker, who spoke to the Herald on the condition of anonymity, said of the three foreign nationals she worked with, just a Taiwanese was deported.
She claimed the other two, who are from the UK, have been working in several Auckland brothels while on temporary visas over two years, have remained "untouched" by INZ.
Between December 2014 and March 2018 there had been a total of 57 complaints to INZ about migrant sex workers.
Last year, INZ deported 827 people by force, of whom 28 per cent were from India, 26 per cent from Tonga, Samoa or Fiji and 6 per cent from European Union countries.
However, a Herald investigation last month found that INZ was forced to stop deporting all but the riskiest illegal immigrants after a budget blowout earlier this year.