Edward Snowden has signed an open letter along with numerous human rights groups asking that Google kill its plan to launch a censored search engine in China.

A group of 14 human rights groups sent a similar letter to Google in August about the so-called Project Dragonfly, but say they received a dissatisfactory response.

The new letter, which has 71 signatories, was published the evening before Google CEO Sundar Pichai is due to testify in front of Congress.

NSA whistleblower Edward Snowden has added his voice to human rights groups asking Google to back out of its plans to launch a censored search engine in China.

In an open letter addressed to Google CEO Sundar Pichai, signed by Snowden and various human rights groups including Amnesty International, the signatories asked Google to kill its plans to re-enter the Chinese market, codenamed "Project Dragonfly."

Snowden signed the most recent letter in his capacity as president of the Freedom of the Press Foundation.

In August, 14 human rights groups penned an open letter to Google asking for it to kill Project Dragonfly, to which Google's Senior Vice President for Global Affairs Kent Walker wrote a reply in October. But in this newest letter, the signatories said they found his response dissatisfactory.

"Google's response – along with further details that have since emerged about Project Dragonfly – only heightens our fear that the company may knowingly compromise its commitments to human rights and freedom of expression, in exchange for access to the Chinese search market," the letter states.

Read more: Google's Dragonfly execs didn't take written notes and isolated internal teams to hide China search plans from other employees

"New details leaked to the media strongly suggest that if Google launches such a product it would facilitate repressive state censorship, surveillance, and other violations affecting nearly a billion people in China," it continued.

The letter pointed to recent media reports which the signatories found troubling, and which in some instances contradicted Walker's letter. For example, the signatories say that while Walker told them the product was not close to launch, a leaked transcript of an internal meeting obtained by The Intercept showed a Google exec saying the product could be "six to nine months [to launch]."

The new letter, which has 71 signatories, came on the eve of Sundar Pichai's testimony to Congress.

Business Insider contacted Google for comment.