TikTok, the short-video app owned by China’s ByteDance, declined to testify at a congressional hearing slated for Tuesday scheduled by Republican Senator Josh Hawley to discuss its business and risks to American consumers.

Hawley had invited TikTok and Apple to testify at the hearing. Apple, too, declined to participate, leading Hawley to question in a tweet whether the two companies have “something to hide”. Hawley didn’t immediately respond to a comment inquiry sent via his website.

“We appreciate Sen. Hawley’s invitation. Unfortunately, on short notice, we were unable to provide a witness who would be able to contribute to a substantive discussion,” a ByteDance spokeswoman said in texted response to a request for comment.

“We remain committed to working productively with Congress as it looks at how to secure the data of American users, protect their privacy, promote free expression, ensure competition and choice among internet platforms, and preserve U.S. national security interests,” she said.

TikTok has become one of very few Chinese-owned apps that achieved success outside of China. TikTok currently ranks first in the entertainment category in the US iPhone app store, according to data provider Sensor Tower.

The viral short-video app, wildly popular among teenagers, has received increasing scrutiny from the U.S. over privacy concerns and censorship by China.

Earlier this year, Chinese gaming company Beijing Kunlun Tech was forced to sell Grindr, the popular gay dating app that it has owned since 2016, after a US government national security panel raised concerns about its ownership. Among the risks the panel considers is whether a deal gives foreigners access to sensitive information about US citizens.

In a letter addressed to the U.S. national security director last month, Senate Minority Leader Chuck Schumer and Senator Tom Cotton, Republican of Arkansas, are calling on intelligence officials to assess the potential risks posed by TikTok.

“With over 110 million downloads in the US alone, TikTok is a potential counter-intelligence threat we cannot ignore,” the senators wrote in their letter.

Reuters reported last week that TikTok’s owner Bytedance is under a national security review on its US$1 billion acquisition of US social media app Musical.ly.

“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. Part of that effort includes working with Congress and we are committed to doing so,” according to a statement by TikTok.