One of Wall Street's biggest banks stopped briefing the head of its subsidiary in mainland China on sensitive company strategy so that the government can't eavesdrop or demand details later. At nearby outposts for other U.S. and European banks, executives are spending tens of millions of dollars to locally house financial data and set up on-site internal controls. Some units are even looking at reshaping balance sheets to stand separate from parent companies.

Those are just some of the many behind-the-scenes machinations taking place inside the Chinese arms of global financial firms as they try to navigate heightened tensions between the world's two largest economies as well as new rules in the name of national security. JPMorgan Chase & Co., Morgan Stanley, and HSBC Holdings Plc are among a long list of banking behemoths that have deep ties and long histories in China.