Hundreds of Google employees have written to the company to protest against plans to build a censored version of its search engine for China and demand more transparency to understand the ethical consequences of their work.

In the letter, which was obtained by The New York Times, employees wrote that the project and Google’s apparent willingness to abide by China’s censorship requirements “raise urgent moral and ethical issues.”

“Currently we do not have the information required to make ethically-informed decisions about our work, our projects, and our employment,” they added.

The letter is circulating on Google’s internal communication systems and is signed by about 1,400 employees, according to three people familiar with the document, who were not authorised to speak publicly.

The internal activism presents another obstacle for Google’s potential return to China eight years after the company publicly withdrew from the country in protest at censorship and government hacking.

China has the world’s largest internet audience but has frustrated US tech giants with content restrictions or outright blockages of services including Facebook and Instagram.

Google’s interest in bringing search back to China came to the forefront earlier this month, when reports surfaced that the company was working on a search app that restricts content banned by Beijing.

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The project, known internally as Dragonfly, was developed largely in secret, prompting outrage among employees who worried they had been unwittingly working on technology that would help China withhold information from its citizens.

“We urgently need more transparency, a seat at the table, and a commitment to clear and open processes: Google employees need to know what we’re building,” the letter said.

Google declined to comment on the letter. It has said in the past that it will not comment on Dragonfly or “speculation about future plans.”

On Thursday, employees pressed Google’s chief executive, Sundar Pichai, and other management about Dragonfly at a weekly staff meeting.

“If we were to do our mission well, we are to think seriously about how to do more in China,” Mr Pichai said in the staff meeting, the audio of which was obtained by The Times. “That said, we are not close to launching a search product in China.”

Mr Pichai and Sergey Brin, a co-founder of Google, stopped answering questions about Dragonfly after seeing their answers posted on Twitter.