HONG KONG — The Chinese government, which has long used its country’s vast market as leverage over American technology companies, is now asking some of those firms to directly pledge their commitment to contentious policies that could require them to turn user data and intellectual property over to the government.

The government distributed a document to some American tech companies earlier this summer, in which it asked the companies to promise they would not harm China’s national security and would store Chinese user data within the country, according to three people with knowledge of the letter who spoke on the condition of anonymity.

The letter also asks the American companies to ensure their products are “secure and controllable,” a catchphrase that industry groups said could be used to force companies to build so-called back doors — which allow third-party access to systems — provide encryption keys or even hand over source code.

The document underlines the way China is wielding its power over the American tech industry. Next week, Beijing has also planned a tech forum in Seattle between China’s Internet czar, Lu Wei, and tech companies including Apple, Facebook, IBM, Google and Uber, in a show of how it can get some of the world’s leading tech players to meet even as President Obama has suggested American companies are being hurt by anticompetitive Chinese practices. The forum is timed to coincide with President Xi Jinping‘s first state visit to the United States.