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Google workers signed a public letter asking their company’s management to cancel controversial plans to build a censored version of the company’s search product in China, referred to as Project Dragonfly.

“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 letter reads. It goes on to state that the project “comes as the Chinese government is openly expanding its surveillance powers and tools of population control” and “would establish a dangerous precedent, at a volatile political moment.”

The letter is in support of Amnesty International’s public campaign against the project, which includes planned protests outside several Google offices today. About nine workers have signed the letter so far, including two of the organizers of the recent Google Walkout protests.

Update: 310 Google employees have signed the letter as of Tuesday evening.

This isn’t the first time Google employees have taken issue with Google’s ambitions to build a censored search app for China. But it’s the first time employees have publicly called for it to end. In August, around 1,400 employees signed a letter internally raising ethical concerns about the project. The app was reportedly designed to blacklist phrases such as “human rights,” “Nobel Prize,” and “student protest,” according to the Intercept, which first reported on its existence. Several employees including a senior research scientist resigned over the issue.

There has also been increasing pressure to end the project from U.S. politicians. Six senators have asked for more information about the project and Vice President Mike Pence publicly criticized the project, saying that it “will strengthen Communist Party censorship and compromise the privacy of Chinese customers” and called on Google to halt development.

Google CEO Sundar Pichai has defended the company’s decision to enter the Chinese market, arguing that the company is always balancing its values when abiding by local laws in other countries.

“We are compelled by our mission [to] provide information to everyone, and [China is] 20 percent of the world’s population.” said Pichai speaking at the WIRED25 conference last month.

Google previously cancelled plans to expand its business to China in 2010 over concerns about the government’s involvement in cyber attacks and regulations on citizens’ free speech.

In the past year, Google employees have become increasingly outspoken about ethical implications of how the company’s technology is used. In April, thousands of employees criticized the company’s involvement in a project with the Pentagon to use Google artificial intelligence technology for military purposes. Two months later, the company decided not to renew that contract.

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