As one of the most popular mobile video apps in the U.S. and the entire world, TikTok has generated enormous usage and downloads in different countries. It is reported to have increased to 500 million monthly active users (MAU), 26.5 million of which are from the U.S.

This sky-rocketing user growth trajectory, however, has met a serious setback due to significant data security challenges and censorship from U.S. lawmakers.

TikTok is facing mounting pressure from both the public and lawmakers over concerns that the app censors content deemed offensive to the Chinese government, accesses users' data without their consent, and poses a threat to U.S. national security.

On Wednesday, Alex Zhu, the head of TikTok, was reported to cancel several meetings with high-powered U.S. senators. Zhu moved the meetings to "after the holidays," even though it's not clear whether another date for these meetings has been scheduled.

In November, TikTok was also asked to testify at a congressional hearing on its relationships with China, but the company declined to send anyone.

Since TikTok's acquisition of the app Musical.ly in 2017 and subsequent merger in 2018, the Chinese mobile app has rapidly become one of the most popular social platforms in the world.

In the past few years, the Committee on Foreign Investment in the United States (CFIUS) has enhanced its scrutiny of China's investments to prevent any potential risks regarding sensitive U.S. data being exposed or apprehended.

CFIUS recently opened an investigation into TikTok regarding possible national security risks. TikTok's relationship with Chinese investments has even prompted a bi-partisan investigation request from Congress.

Since TikTok did not include CFIUS in the Musical.ly deal in 2017, the Committee has grounds to investigate the deal, specifically looking for how China's influence and practices could affect national security.One major aspect of the Committee investigation could include TikTok's potential failure to protect consumer data by not implementing strong enough collection methods or storage practices that satisfy U.S. standards.

TikTok operates in the U.S. and claims that it stores all U.S. data within the country, but the holding company ByteDance is still subject to Chinese regulations and laws. Because the parent company resides in a non-U.S. jurisdiction, many security and regulators in the U.S. government are concerned that the data is not as safe as the company claims and instead, could fall victim to China's laws, procurement, influence, and censorship.

In an internal memo, Zhang Yiming, CEO of TikTok parent ByteDance, urged the company to focus on adding users in a wider range of markets as a means of pre-empting potential risks in the U.S. market and diversifying TikTok's growth. Yiming also detailed TikTok's need to improve user data protection, as well as better manage global public affairs and branding.

ByteDance, who is backed by SoftBank Group (SFTBY  ), is planning to go public on Hong Kong Stock Exchange by the first quarter in 2020.