"Prostitution needs to be governed in New Zealand. If there is a legislation, there should be a Minister."
The letter claimed migrants coming on temporary visas to work as prostitutes were "taking money off legal sex workers, not paying tax and going home with the money".
Although New Zealanders are able to work as prostitutes since 2003, it is illegal for people on temporary visas to do sex work.
"NZPC's current focus is legalising internationals to be allowed to provide commercial sexual services here in New Zealand and no legal New Zealand sex worker wants this."
Bob McCoskrie, Family First national director, said they shared a common ground in agreeing that NZPC shouldn't be getting government funding.
The collective gets $1,099,944 excluding GST annually through the Ministry of Health for funding of services to sex workers, including those unlawfully in New Zealand.
Family First is highly critical of the Prostitution Reform Act and is calling for a Nordic model for the law.
"Banning of street prostitution, prosecution of the buyer, while helping women and men out of the industry," McCoskrie explained.
McCoskrie however did not put his name on the open letter.
"(Lewis) says that prostitutes don't think NZPC should be getting government funding and isn't representing the best interests of workers," he said.
"So we gave her some hints on doing an open letter."
NZPC's Dame Catherine Healy said the collective was against law that discriminated against sex workers and which impacted harmfully on the occupational safety and health and human rights of sex workers.
"NZPC feels it has a responsibility to ensure all sex workers are able to access its services in light of public health concerns," Healy said.
She said the collective worked with sex workers from all sectors but always advised them to work within the law.
The Prime Minister's office has been approached for comments.
