A bipartisan group of 16 U.S. lawmakers asked Alphabet Inc's Google on Thursday if it would comply with China's internet censorship and surveillance policies should it re-enter the Chinese search engine market.

The questioning added to the pressure on Google to disclose precautions it would take to protect the safety of its users if Chinese regulators allow its search engine to operate.

More than 1,000 Google employees, six U.S. senators and at least 14 human rights groups have written to the company expressing concern about its China ambitions.

On Thursday, Jack Poulson, a research scientist who had worked for Google for more than two years, said he resigned because he felt the company was not honoring its commitment to human rights norms in designing the search app.

Poulson told Reuters that executives would not specify to him where the company would draw the line on agreeing to Chinese demands.

"Unfortunately, the virtually unanimous response over the course of three very vocal weeks of escalation was: 'I don't know either,'" Poulson said.

A bipartisan group of 16 US lawmakers yesterday sent out a letter to Google CEO @SundarPichai demanding answers about the company's China censorship plan, which they say causes them "serious concerns." Here's the letter: pic.twitter.com/1GI8eG9fgh — Ryan Gallagher (@rj_gallagher) September 14, 2018

He was among a handful who resigned, he told the Intercept online publication, which first reported on his action.

Google declined to comment directly on the lawmakers' letter or the resignations but said in a statement it had been “investing for many years to help Chinese users" and described its "work on search" for China as "exploratory" and "not close to launching."

Reuters reported last month that Google planned to seek government clearance to provide a version of its search engine in China that blocks some websites and search terms.

Members of the U.S. House of Representatives, including liberal Democrats and conservative Republicans, said in their letter on Thursday they had "serious concerns" about the potential step.

The letter asked if Google would "ensure that individual Chinese citizens or foreigners living in China, including Americans, will not be surveilled or targeted through Google applications."

Representative David Cicilline, a Democrat and signer of the letter, wrote on Twitter that "Google should not be helping China crack down on free speech and political dissent."

Other signers include Representative Michael McCaul, a Republican who chairs the House Homeland Security Committee.

The company could face questions about China when it testifies on privacy issues before a Senate panel on Sept. 26.

House Majority Leader Kevin McCarthy, a Republican, said on Tuesday that Google would be invited to testify on a number of issues. He wrote on Twitter that Google had worked with China and Russia on censorship but no longer wanted to do a technology deal with the U.S. Defense Department.

Google's main search platform has been blocked in China since 2010, but it has been attempting to make new inroads into the world's largest smartphone market by users.

Google's re-entry is not guaranteed as China has stepped up scrutiny of business dealings involving U.S. tech firms including Facebook Inc and Apple Inc amid intensifying trade tensions between Beijing and Washington.