Staff at Google have called on the search giant to end work on a controversial search engine project for China.
Called Dragonfly, the search engine would be a censored version developed with the aid of the Chinese government.
In a letter published online, 60 employees said the project would only help state surveillance.
Their call to cancel was backed by Amnesty International which said it was at odds with the company's values.
Once completed, Dragonfly would "enable censorship" and help the Chinese government's disinformation campaigns, claimed the letter.
China made significant use of technology to stifle freedom of expression and repress dissent, said the group.
"Dragonfly in China would establish a dangerous precedent at a volatile political moment, one that would make it harder for Google to deny other countries similar concessions," wrote the employees.
The group said the Chinese government would benefit from Dragonfly going live.
"We object to technologies that aid the powerful in oppressing the vulnerable, wherever they may be," said the open letter.
So far, they said, Google's response to protests and complaints by thousands of workers, rights groups and journalists had been "unsatisfactory".
"Google staff don't want to be part of the great firewall of China," said Anna Bacciarelli, Amnesty International's researcher on technology and human rights.
Ms Bacciarelli said thousands of employees did not support work on the project. In August, more than 1,400 Google staff called on it to do a better job of policing ethically troubling development jobs.
Amnesty organised protests outside Google offices to collect signatures for a petition calling on the firm to drop Dragonfly.
Google declined to comment directly on the letter and said its work with China on a search engine was "exploratory".