New documents filed with the federal appeals court in Washington late Friday said an internal ByteDance workplace and communications program called Lark connected employees in China and the United States and was used to send data on U.S. users, including personally identifiable information.

The search tool inside Lark would have allowed ByteDance and TikTok employees “to collect bulk user information based on the user’s content or expressions, including views on gun control, abortion, and religion,” a DOJ official said. The filing did not indicate how or if the data was used.

In April, President Biden signed a law forcing ByteDance to sell TikTok to a non-Chinese company or face a ban in the United States, where it has 170 million users. The documents filed Friday were the government’s first major response to a legal challenge brought by TikTok and ByteDance.

TikTok spokesman Alex Haurek said early Saturday that the company remained “confident we will prevail in court.”

In a statement published on X, TikTok added that a ban on the app would violate its users’ First Amendment rights. “Nothing in this brief changes the fact that the Constitution is on our side. The TikTok ban would silence 170 million Americans’ voices, violating the First Amendment.”

Social media companies, like Meta’s Facebook, also ask users to share their religion and other personal information. However the DOJ alleges that TikTok’s access to sensitive information could cause geopolitical risks, by allowing the Chinese government to demand ByteDance share U.S. users’ data.

The department stated that TikTok’s algorithm, which determines the videos users see, “can be manually manipulated, and its location in China would permit the Chinese government to covertly control the algorithm — and thus secretly shape the content that American users receive — for its own malign purposes.”

“The serious national-security threat posed by TikTok is real, as evidenced by the public record and confirmed by classified information supplied by the intelligence community,” the government argued in another filing.

“TikTok provides the Chinese government the means to undermine U.S. national security in two principal ways: data collection and covert content manipulation,” it added.

The documents filed late Friday were heavily redacted, and Justice Department officials have said they intend to give the court an unredacted version of their legal brief featuring classified information. Judges could review that brief, but not the companies or the general public.

China has said it will block the sale of TikTok’s algorithm, and TikTok and ByteDance’s lawsuit claims the challenge of replacing such a central part of the app’s structure “is not remotely feasible” before the January deadline.

In May, eight TikTok creators sued the U.S. government over the law, which they said violated their First Amendment rights. TikTok, which is funding their action, has consolidated the two cases into one lawsuit.

The department responded to this by saying that users would still be able to post and view the same content on other social media platforms if TikTok were taken down.

“Any preference these petitioners may have for using TikTok over those other platforms does not create a constitutional right to TikTok,” it said, “nor could their preference overcome the national-security interests supporting the Act.”

Responding to TikTok’s argument that the U.S. had offered no proof for its claims of Chinese government influence, the Justice Department said in its brief that the U.S. “is not required to wait until its foreign adversary takes specific detrimental actions before responding to such a threat.”

“Congress can act even if all of the threatened harms have not yet broadly materialized or been detected,” officials wrote.

DOJ officials also argued against TikTok’s First Amendment defense, saying any damage from the law to users’ speech freedoms would be “incidental.”

“Any adverse effects on expression by U.S. persons are indirect and amply justified,” officials said. TikTok creators, they added later, “have no First Amendment right to TikTok.”