A group of engineers and managers at Google have published an open letter calling for the company to end its development of a censored search engine designed for the Chinese market. The letter marks an escalation in earlier protests against the product, codenamed Project Dragonfly.

The publication of the letter coincides with human rights group Amnesty International launching a public petition calling on Google to cancel the project. The non-profit organisation has said it will encourage Google workers to sign the petition by targeting them with advertising on LinkedIn and protesting outside Google offices.

“This is a watershed moment for Google,” said Joe Westby, researcher on technology and human rights at Amnesty International. “As the worlds number one search engine, it should be fighting for an internet where information is freely accessible to everyone, not backing the Chinese governments dystopian alternative.”

Over the past few years, Google has expressed more and more interest in regaining access to Chinese consumers. It has partnered with local firms in a variety of areas and launched small products like games, but last month, it was revealed that the internet giant is hard at work on a new version of its core search product that will meet the censorship requirements of Chinese authorities.

This news was met with criticism by human rights and free speech advocates, and came just two months after 1,400 Google workers urged the company to improve its oversight on ethically questionable projects.

“We are among thousands of employees who have raised our voices for months,” says the open letter. “Our opposition to Dragonfly is not about China: we object to technologies that aid the powerful in oppressing the vulnerable, wherever they may be.

“The Chinese government certainly isnt alone in its readiness to stifle freedom of expression, and to use surveillance to repress dissent. 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.”

The letter was originally signed by 11 Google employees, but is being updated as more add their voices to the cause. At time of publication, there were 91 names supporting the statement and calling for Google to cease work on Dragonfly.