Amnesty International and more than 300 Google employees have launched the biggest campaign to date calling on the search giant and CEO Sundar Pichai to abandon controversial plans to return to the Chinese market.

Google employees circulated a petition on the blogging site Medium and set up a new Twitter account, Googlers against Dragonfly, to publicize their efforts to shut down development on a filtered search engine tailored for China, codenamed Project Dragonfly. Amnesty also put up its own petition and launched a satirical ad campaign directed at Pichai calling for job applicants to work on the search engine. On Tuesday, the human rights group even published photos on Twitter purportedly showing its members visiting Google offices in several countries to stage protests.

Google's plan to launch a new censored China search was first disclosed in August, marking a major turnaround after the company shuttered its China search engine in 2010 over Beijing's rigid requirements. One major change during Google's eight-year absence was the rapid rise of the company's Android operating system, which powers the majority of China's hundreds of millions of smartphones. Android systems typically include easy access to various Google products and services in other parts of the world, but are largely absent in China.

Read more: Google CEO Says China Search Engine Project Was ‘Experiment’