Facebook has secretly developed a censorship tool as part of its efforts to re-enter the Chinese market, The New York Times reported on Tuesday. Chief Executive Officer Mark Zuckerberg has supported and defended the development of the software, according to the report.

The social media giant is likely to offer the tool to a partner Chinese company, allowing it to censor content and monitor popular stories and subjects that are shared across the network, according to the report. The partner company will then have full control to decide whether the posts and other content should appear in people’s Facebook feeds. The software will also allow specific content to be blocked from appearing in the feeds of users’ in certain geographic areas.

The tool is one of the numerous ideas the company is discussing in connection with its agenda to be re-introduced in China, according to The New York Times. Several employees are believed to have resigned after expressing their concerns about the project. There have also been no signs that the software has been offered to Chinese authorities.

A Facebook spokesperson said the company had not finalised its approach to re-entering China. “We have long said that we are interested in China and are spending time understanding and learning more about the country,” the spokesperson said.

The social media website was banned in China in 2009 following riots in Urumqi, the capital of the Xinjiang Uighur Autonomous Region in the north-western party of the country. The company, which blocked around 55,000 pieces of content in 20 countries between July 2015 and December 2015, has also been grappling with what kind of content to allow on its platform, following the election of Donald Trump as the United States president-elect.