Musical.ly, the social networking app now known as TikTok, illegally gathered and used children’s personal data, and must now pay a $5.7million fine for violating the Children’s Online Privacy Protection Act (COPPA), the Federal Trade Commission (FTC) said Wednesday.

The operators of Musical.ly, which allows users to make and share short, lip-synced videos, “knew many children were using the app but they still failed to seek parental consent before collecting names, email addresses, and other personal information from users under the age of 13,” FTC Chairman Joe Simons said in a release announcing the fine, the largest yet under COPPA. “This record penalty should be a reminder to all online services and websites that target children: We take enforcement of COPPA very seriously, and we will not tolerate companies that flagrantly ignore the law.”

Many of the users were under 13 years old, which the app operators knew, yet they didn’t notify parents that their children’s personal data was being collected and used – nor did they seek parental consent. The FTC said Musical.ly failed to delete the personal data in a timely manner. The Justice Department filed the complaint in the U.S. District Court Central District of California on behalf of the commission, which voted 5-0 to approve the consent decree.

Calling the settlement “a big win in the fight to protect children’s privacy, FTC Commissioners Rohit Chopra and Kelley Slaughter, said in a separate statement, “When any company appears to have a made a business decision to violate or disregard the law, the Commission should identify and investigate those individuals who made or ratified that decision and evaluate whether to charge them.”

They said investigators “should prioritize uncovering the role of corporate officers and directors and hold accountable everyone who broke the law.”