Washington DC - The US, in a lawsuit on Friday, accused TikTok of violating children's privacy by collecting data about them without their parents' permission when they use the app.

The Department of Justice and Federal Trade Commission (FTC) joined forces in a civil suit, saying the popular video-snippet-sharing app broke the Children's Online Privacy Protection Act (COPPA).

"TikTok knowingly and repeatedly violated kids' privacy, threatening the safety of millions of children across the country," FTC chair Lina Khan said in a release.

COPPA bars websites from gathering personal information about children younger than 13 years of age without getting parental permission.

The suit argues that since 2019, TikTok has allowed children to use the app, collecting and using personal data from young users without letting their parents know.

Even accounts created in a "Kids Mode" intended for users younger than 13 gathered email addresses and other personal information, the suit contends.

TikTok and its parent company ByteDance often "failed to honor" requests by parents to have their children's accounts and data removed and had ineffective policies for identifying and deleting accounts created by children, Justice Department officials said in the release.

"This action is necessary to prevent the defendants, who are repeat offenders and operate on a massive scale, from collecting and using young children's private information without any parental consent or control," Justice Department deputy assistant attorney Brian Boynton said in the release.

Five years ago, the US filed a COPPA-focused suit against an app called Musical.ly, which China-based ByteDance had bought and merged into TikTok.

That case resulted in TikTok having to take steps to comply with the Children's Privacy Act, according to Justice Department officials.

TikTok's collection of user data makes it a national security threat, the Justice Department said a week ago in response to a ByteDance legal bid to the forced sale of the app.

TikTok's suit in a Washington federal court argues that a law that forces the app to be sold next year or face a US ban violates First Amendment rights of free speech.

The US response counters that the law addresses national security concerns, not speech, and that TikTok's Chinese parent company ByteDance is not able to claim First Amendment rights in the US.

"Given TikTok's broad reach within the United States, the capacity for China to use TikTok's features to achieve its overarching objective to undermine American interests creates a national-security threat of immense depth and scale," the Justice Department wrote in its filing.

The legal response to TikTok's suit in an appeals court details concerns that ByteDance could, and would, comply with Chinese government demands for data about US users or yield to pressure to censor or promote content on the platform, senior justice department officials said in a briefing.

TikTok countered in a filing, saying, "The Constitution is on our side."

"The TikTok ban would silence 170 million Americans' voices, violating the First Amendment," the company said in a statement on social media platform X, referring to the app's users in the US.

"As we've said before, the government has never put forth proof of its claims, including when Congress passed this unconstitutional law."

A bill signed by President Joe Biden early this year set a mid-January 2025 deadline for TikTok to find a non-Chinese buyer or face a US ban.

ByteDance has said it has no plans to sell TikTok, leaving the lawsuit, which will likely go to the Supreme Court, as its only option to avoid a ban.

"There is no question: the Act will force a shutdown of TikTok by January 19, 2025," the lawsuit said, "silencing [those] who use the platform to communicate in ways that cannot be replicated elsewhere."