The chair of a U.S. congressional panel wrote to Alphabet’s (GOOGL.O) Google and to Apple (AAPL.O) on Friday to ask what if any disclosures mobile apps are required to make regarding overseas ties, a concern that follows reports of Chinese investment in popular apps such as TikTok and Grindr.

Axar.az reports citing Reuters that Rep. Stephen Lynch, chairman of a subcommittee of the House of Representatives Oversight Committee, said in a statement that he had asked both Google and Apple to tell Congress whether they required app developers to disclose any non-U.S. ties.

Concern over China acquiring sensitive data about U.S. citizens through social media apps is one of several sore areas in relations between the United States and China even as U.S. President Donald Trump’s trade war with China fans suspicion between the world’s two largest economies.

TikTok, which is wildly popular with teenagers, is owned by Chinese technology company ByteDance. In a related matter, the Chinese gaming company Beijing Kunlun Tech Co Ltd has said it would sell popular gay dating app Grindr Inc by June 2020 because of U.S. national security concerns.