The United States has opened a national security review into TikTok’s parent company over its acquisition of social media app Musical.ly, Reuters reports.

TikTok acquired Musical.ly in 2017

In 2017, China-based TikTok owner ByteDance bought up the popular lip-syncing app — and its user base — for $1 billion. Last year, the app was fully rebranded as part of TikTok.

But in the time since the deal closed, TikTok has faced substantial pressure from US lawmakers who have questioned how the company moderates its political content and stores its user data.

In a letter last month, Sen. Marco Rubio (R-FL) called for an investigation into the company, writing that “Chinese-owned apps are increasingly being used to censor content and silence open discussion on topics deemed sensitive by the Chinese Government and Community Party.” The letter followed reports that TikTok was censoring political content that was offensive to the Chinese government. (The company has said its moderation decisions are based in the US and “are not influenced by any foreign government.”) Rubio’s note was followed by one from Sens. Tom Cotton (R-AR) and Chuck Schumer (D-NY) also calling for a review.

According to Reuters, the US has now launched such a review through the Committee on Foreign Investment in the United States, or CFIUS, which is responsible for reviewing deals with national security implications. The news service reports that TikTok did not go through a CFIUS review when it made the Musical.ly acquisition, and are in talks about national security concerns now. The New York Times has since corroborated Reuters’s reporting.

The investigation is the latest hurdle for the company, which has dealt with intense scrutiny as the tech industry as a whole faces renewed questions about Chinese censorship online. Last month, in one notable example, Apple was criticized for pulling an app used by pro-democracy protestors in Hong Kong.

“While we cannot comment on ongoing regulatory processes, TikTok has made clear that we have no higher priority than earning the trust of users and regulators in the US,” a company spokesperson told The Verge in a statement. “Part of that effort includes working with Congress and we are committed to doing so.”