The wildly popular TikTok app continues to come under pressure from U.S. lawmakers.

Many are concerned that ByteDance, the Beijing-based company behind the app, has close ties with the Chinese government, and that laws in China mean it could be required to hand over user data to the government to assist in intelligence gathering.

There are also fears that the app’s algorithms could be tweaked to push particular content designed to further Chinese interests.

In a letter shared on Thursday, Michael Bennett, a Democratic senator from Colorado, called on the CEOs of Apple and Google to remove TikTok from their app stores at the earliest opportunity.

Also a member of the Senate Intelligence Committee, Bennett said in the letter that no company subject to “Chinese Communist Party dictates should have the power to accumulate such extensive data on the American people or curate content to nearly a third of our population.”

Bennett added: “Beijing’s requirement raises the obvious risk that the Chinese Communist Party (CCP) could weaponize TikTok against the United States, specifically, by forcing ByteDance to surrender Americans’ sensitive data or manipulate the content Americans receive to advance China’s interests. These obvious risks render TikTok, in its current form, an unacceptable threat to the national security of the United States.”

ByteDance has always insisted that user data is not stored inside China and so is out of reach of the Chinese authorities. In August last year, the company submitted a plan to the U.S. government explaining its measures for handling and protecting the data of U.S.-based users, but the Biden administration has yet to respond.

Tightening its grip on TikTok, Congress passed a bill toward the end of 2022 banning the app from government devices.

Around half of the states in the U.S. have already banned TikTok from state-owned devices. A growing number of U.S. universities are also banning the app from school-owned devices. On January 24, Sen. Josh Hawley, R-Missouri, said he planned to introduce a bill to ban TikTok, describing the app as “China’s backdoor into Americans’ lives.”

TikTok has come under increasing scrutiny over recent years. In 2020, then-president Donald Trump signed an executive order banning TikTok in the U.S. But the ban faced legal challenges that stopped it from coming into force.

Of course, a vast number of Americans have already downloaded the app, but removing it from the app stores would make it more difficult for users to receive software updates to fix bugs and add new features. A widespread ban would likely benefit TikTok rivals such as Instagram and Snapchat, which have already been adding TikTok-like features to their apps to try to attract more users.