Apple and the Chinese-owned music-video app TikTok are threats to international data security because of their business ties to China, a key Republican senator warned.

“With Apple and TikTok, we see two sides of the same coin when it comes to data security: the danger of Chinese tech platforms’ entry into the US market, and the danger of American tech companies’ operations in China,” Missouri lawmaker Josh Hawley told a hearing he led on big data and China on Tuesday.

Hawley, a frequent tech critic and ally of President Donald Trump, held the hearing as security concerns mount around TikTok. A US security panel has begun to review the purchase of social media startup by China’s ByteDance Inc. for almost $1 billion two years ago to merge it with TikTok, Bloomberg News reported last week.

US lawmakers called for a national security review of TikTok last month. Senate Minority Leader Chuck Schumer of New York and Republican Senator Tom Cotton of Arkansas wrote to US Acting Director of National Intelligence Joseph Maguire Oct. 23, referring to TikTok as a “potential counter intelligence threat we cannot ignore.”

“A company compromised by the Chinese Communist Party knows where your children are, knows what they look like, what their voices sound like, what they are watching and what they share with each other,” Hawley said during the hearing. “All it takes is one knock on the door of their parent company, based in China, from a Communist Party official, for that data to be transferred to the Chinese government’s hands whenever they need it.”

Hawley said on Twitter he invited both TikTok and Apple to appear at the hearing, but they declined. He singled out TikTok, saying the company “has refused to join the hearing and provide more info on how it handles Americans’ personal data.” He told reporters after the hearing that it “may be necessary” to subpoena TikTok.

“We have no higher priority than earning the trust of users and regulators in the US,” a TikTok representative said in a statement. “Part of that effort includes working with Congress and we are committed to doing so.” TikTok said it hadn’t been able to provide a witness who would have been prepared “to contribute to a substantive discussion” on short notice.

The company’s content decisions often came from Chinese leadership as recently as this spring, according to unnamed former employees interviewed in a Tuesday report in the Washington Post. In a letter to Hawley released by his office, TikTok General Manager Vanessa Pappas said content moderators are led by a US-based team and would not take direction from Beijing.