The head of the FBI says the bureau has "national security concerns" about the U.S. operations of TikTok, warning that the Chinese government could potentially use the popular video-sharing app to influence American users or control their devices.

The FBI has "a number of concerns," director Christopher Wray told a House Homeland Security Committee hearing about worldwide threats on Tuesday, just days after Republican lawmakers introduced a bill that would ban the app nationwide.

"They include the possibility that the Chinese government could use it to control data collection on millions of users or control the recommendation algorithm, which could be used for influence operations if they so chose, or to control software on millions of devices, which gives it an opportunity to potentially technically compromise personal devices," Wray said.

TikTok, which hit 1 billion monthly active users in September 2021, is owned by the Chinese company ByteDance. Chinese national security laws can compel foreign and domestic firms operating within the country to share their data with the government upon request, and there are concerns about China's ruling Communist Party using this broad authority to gather sensitive intellectual property, proprietary commercial secrets and personal data.

TikTok has long said that it stores U.S. user data within the U.S. and does not comply with Chinese government content moderation requirements. But the company has come under increasing scrutiny in recent months, and in July it acknowledged that non-U.S. employees did in fact have access to U.S. user data.

Citing leaked meeting audio, Buzzfeed News reported in June that China-based ByteDance employees have repeatedly accessed non-public data (like phone numbers and birthdays) of U.S. TikTok users. Separately, Forbes reported in October that ByteDance planned to use TikTok "to monitor the personal location of some specific American citizens," which the company denied.

Wray said at the hearing that Chinese law essentially requires companies to "do whatever the government wants them to in terms of sharing information or serving as a tool of the Chinese government."

"And so that's plenty of reason by itself to be extremely concerned," he added.

The FBI has in the last few years been shifting its focus to China. In July, Wray said China was the "biggest long-term threat to our economic and national security" and accused Beijing of having interfered in recent elections.

U.S. concerns over TikTok are not new

Various government officials have issued similar warnings over the years, and two presidential administrations have tried to address these security concerns in different ways.

The Committee on Foreign Investment in the United States (CFIUS), which conducts national security reviews of foreign companies' deals, ordered ByteDance to divest from TikTok back in 2020. Then-President Donald Trump tried to have the app shut down in the U.S. unless it spun off from ByteDance, but faced challenges in court.

President Biden paused those efforts when he took office, but his administration has continued to engage in national security negotiations with the company. The New York Times reported in September that CFIUS and TikTok had reached a preliminary agreement on safeguards that would satisfy the U.S.

When asked at Tuesday's hearing about what action the U.S. is taking, Wray said that discussion is more appropriate for a classified setting. But he did say that the FBI's foreign investment unit is involved in the CFIUS process.

"Our input would be taken into account in any agreements that might be made to address the issue," he added.

A TikTok spokesperson confirmed that in a statement emailed to NPR on Wednesday, adding that the proposed agreement goes beyond data security to address issues like governance, content moderation and algorithmic transparency.

"As Director Wray specified in his remarks, the FBI's input is being considered as part of our ongoing negotiations with the U.S. Government," the spokesperson wrote. "While we can't comment on the specifics of those confidential discussions, we are confident that we are on a path to fully satisfy all reasonable U.S. national security concerns."

Some lawmakers are pushing for a ban

The idea of a TikTok ban appears to be gaining traction once again.

In late October, Senate Intelligence Committee Chairman Mark Warner (D-Va.) said that the app posed privacy and security concerns to Americans — and went a step further by praising Trump's approach.

"This is not something you would normally hear me say, but Donald Trump was right on TikTok years ago," Warner told Australia's Sydney Morning Herald. "If your country uses Huawei, if your kids are on TikTok ... the ability for China to have undue influence is a much greater challenge and a much more immediate threat than any kind of actual, armed conflict."

A week later, Federal Communications Commissioner Brendan Carr called on the government to ban TikTok in an Axios interview. (In June, he urged Apple and Google to remove it from their app stores, citing its "pattern of surreptitious data practices.")

Last week, Sen. Marco Rubio and Rep. Mike Gallagher — both Republicans — introduced legislation that they said would ban TikTok "and other social media companies that are effectively controlled by the CCP from operating in the United States."

They outlined their motivations and concerns in a recent Washington Post op-ed.

For one, the lawmakers said the app can track users' locations and collect internet browsing data even from unrelated websites — adding that Beijing could develop profiles on millions of Americans for blackmail or espionage purposes, as well as collect sensitive national security information from U.S. government employees.

They also worried about potential abuses of TikTok's algorithm, and specifically that it could "be used to subtly indoctrinate American citizens" by censoring some videos and promoting others.

"TikTok has already censored references to politically sensitive topics, including the treatment of workers in Xinjiang, China, and the 1989 protests in Tiananmen Square," they wrote. "It has temporarily blocked an American teenager who criticized the treatment of Uyghurs in China. In German videos about Chinese conduct toward Uyghurs, TikTok has modified subtitles for terms such as 'reeducation camp' and 'labor camp,' replacing words with asterisks."

The lawmakers called this an especially frightening prospect given how many adults get their news from TikTok.

But is it the best solution?

Aynne Kokas, a professor of media studies and the director of the East Asia Center at the University of Virginia, describes TikTok as both an entertainment platform and a form of critical communications infrastructure.

And she says it is "part of a larger Chinese government effort to expand extraterritorial control over digital platforms."

"This is something that's been very clearly articulated time and time again, from the 2010 white paper on the internet in China all the way to the 2020 Hong Kong national security law, which allows oversight of national security interests outside of China," she tells NPR's Morning Edition.

That's why she doesn't think that banning TikTok is the best solution — in fact, she compares it more to playing a game of whack-a-mole as China continues to expand its digital territory (TikTok is the most popular Chinese app used by Americans, though there are others, like WeChat).

"When we look at all of these wide-ranging apps that are connected to Chinese firms, it's actually almost nonsensical to ban just one when we see platforms in areas like precision agriculture, communications, gaming, all connected to Chinese firms," she says. "So what's really important is to develop more robust data privacy regulations in the United States to protect users."