Immigration NZ wrote to thank Junlhon and two others for their assistance in prosecuting the alleged smuggler, but told them in the same letter that they have until the end of this month to leave the country.
Last month, Junlhon gave evidence against Auckland woman Wimonrat Konsaijan, who she alleged charged her 275,000 baht ($11,000) for New Zealand visas and air tickets.
The prosecution failed when Justice Christopher Allan ruled the law did not make it a crime to smuggle paying migrants into New Zealand with fraudulently obtained visas.
"This ruling highlighted a potential gap in New Zealand's legislation," said Immigration NZ fraud investigator John Marston, in a letter to the three Thai whistleblowers last week.
"I would like to thank you on behalf of the department and myself personally for all your assistance in the investigation of this case. I appreciate it would not have been easy for you to come forward to report this matter to the authorities."
Junlhon said she had worked eight years in Taiwan, and had hoped to go to Australia for more work - but instead Konsaijan got her a New Zealand visa.
"I have nine brothers and sisters that rely on me. I was prepared to go anywhere for work," she said.
Junlhon's friend, Peeraya Sanmao, and two other migrants say they too paid hundreds of thousands of baht. Sanmao said she was told New Zealand was a good opportunity for a single mother, so she borrowed 235,000 baht from family and friends for a visa and tickets.
"As far as I knew I would be travelling to New Zealand legally to get work," she said. "I trusted Wimonrat."
Junlhon, disappointed at the alleged deception, fronted up to Immigration NZ to blow the whistle. She revealed she been brought in on a visitor's visa that was obtained under false pretences. The forms included a false employment history, and claimed she was married to a man who she met for the first time at Bangkok airport.
Wimonrat Konsaijan was charged with the crime of migrant smuggling. But last month, her High Court trial was called off and Konsaijan was discharged.
A source said Konsaijan was not the mastermind - but immigration investigators had hoped she would lead them to the brains behind a major smuggling route.
Her defence lawyer, Simon Lance, said: "My client is not the one responsible. I think there is a bit more than meets the eye. She made a very modest commission to help them with their travel arrangements. A lot of the money went to expenses, hotels and flights."
Konsaijan has also been ordered to leave the country, but hopes to reapply for a visa from Thailand, before returning to Auckland to be with her partner, a New Zealander. "She's met a man here and, yes, he's keen to explore those options," Lance said.
Under the Crimes Act, someone can be jailed for 20 years for "arranging for an unauthorised migrant to enter New Zealand for a material benefit, knowing or being reckless as to whether they were a recognised migrant". But because the visas were legitimate - albeit obtained under false pretences - Konsaijan committed no crime.
NZ First leader Winston Peters said the same loophole could extend to this year's visas-for-cash scams, involving thousands of Tongan and Chinese. It was outrageous that key witnesses who were "genuine victims" were being sent home and would be in danger. "We owe them better than this."
Labour's immigration spokeswoman, Darien Fenton, said victims of immigration scams would now be too scared to come forward.
Tuariki John Delamere, a former immigration minister-turned-adviser, said the Crown's incompetence was "mind-boggling and embarrassing".
