The app, which lets you make short videos lip-syncing or dancing to songs, is owned by China-based ByteDance.
Sens. Chuck Schumer and Tom Cotton on Wednesday sent a letter to Acting Director of National Intelligence Joseph Maguire requesting an inquiry into "national security risk" posed by TikTok, a popular social video app owned by Chinese company ByteDance.
The mobile app, which lets users share clips of themselves lip-syncing or dancing to popular music, reportedly has more than a billion downloads, with millions of those in the US. The senators expressed concern that the Chinese government could force ByteDance to turn over US user data and called the app a "counterintelligence threat we cannot ignore."
"While the company has stated that TikTok does not operate in China and stores US user data in the US, ByteDance is still required to adhere to the laws of China," the senators wrote. "Without an independent judiciary to review requests made by the Chinese government for data or other actions, there is no legal mechanism for Chinese companies to appeal if they disagree with a request."
In a blog post responding to the letter on Thursday, TikTok said all US user data is stored in America with backup redundancy in Singapore.
"Our data centers are located entirely outside of China, and none of our data is subject to Chinese law," the company wrote. "Further, we have a dedicated technical team focused on adhering to robust cybersecurity policies, and data privacy and security practices."
The senators also said questions have been raised about censorship of content on the app, as well as concerns about the platform being the target of foreign influence campaigns like the one carried out by Russia during the 2016 election.
The senators requested a congressional briefing on the intelligence community's findings.
TikTok has faced scrutiny before over its handling of data, though that's largely focused on the app's popularity with teens and kids. In February, TikTok paid $5.7 million to settle US Federal Trade Commission charges that it illegally collected personal information from children. The UK is also now reportedly examining how TikTok handles children's data and whether it ensures child safety on its platform.
Originally published Oct. 24, 8:17 a.m. PT.
Updates, 8:52 a.m.: Adds more details from the senators' letter; 9:06 a.m.: Includes comment from TikTok; 1:46 p.m.: Adds more background and additional comment from TikTok.