At issue is whether ByteDance violated any laws by inappropriately gathering the data of some users, including journalists who cover tech firms

It was not clear what potential federal crimes were at issue, but the Justice Department’s fraud section is involved in the investigation, these people said.

Forbes first reported the news.

U.S. security agencies and lawmakers have increasingly complained that the company is too closely aligned with the Chinese government and could use the service to track Americans and push pro-China propaganda.

In December, ByteDance said it fired four employees after an internal investigation found they had accessed data on two journalists. The investigation found that the employees pulled IP addresses and other data in an attempt to identify who might have shared documents with journalists for BuzzFeed News and the Financial Times.

“We have strongly condemned the actions of the individuals found to have been involved, and they are no longer employed at ByteDance,” TikTok spokeswoman Jennifer Banks said Friday in a statement. “Our internal investigation is still ongoing, and we will cooperate with any official investigations when brought to us.”

The Biden administration has begun to push ByteDance to sell TikTok, whose ties to China have caused bipartisan unease, even though little evidence has emerged that TikTok poses a national security threat. That push for divestiture is at the recommendation of the Committee on Foreign Investment in the United States, which recently approached TikTok with the plan after over two years of negotiations.

The White House has also endorsed a bipartisan bill that would grant the Commerce Department broad authority to ban or limit TikTok — although efforts to ban the app, which has more than 100 million users, could face the same challenges encountered by the Trump administration, which made similar attempts three years ago. During that bid, federal judges ruled that government did not provide enough evidence that the app presented enough national security risks to outweigh First Amendment rights to free expression.

Biden’s TikTok plan echoes failed Trump bid China called a ‘smash and grab’

TikTok has argued against divestiture. Instead, the company has pushed for strict government oversight, including third-party protection and review of the app’s data and code. The company has argued that its plan would address data privacy and oversight issues better than a forced sale.

This month, however, one former TikTok employee told The Washington Post that the company’s plan, called Project Texas, was flawed and could still leave users’ data exposed. TikTok officials said that some of the employee’s allegations were “unfounded” and that their plan had evolved since the employee’s departure.

Next week, ByteDance chief executive Shou Zi Chew is expected to testify before Congress. TikTok has made serious efforts in recent months to push back on lawmakers’ claims that it poses national security threats. Meanwhile, the federal government — and about two dozen states — have banned the app on government devices.

Cat Zakrzewski contributed to this report.