Booming social media application TikTok needs to pay up in Europe for violating children’s privacy.

The popular Chinese-owned app failed to protect children’s personal information by making their accounts publicly accessible by default and insufficiently tackled risks that under-13 users could access its platform, the Irish Data Protection Commission (DPC) said in a decision published Friday.

The regulator slapped TikTok with a €345 million fine for breaching the EU’s landmark privacy law, the General Data Protection Regulation (GDPR).

The penalty comes amid high tensions between the European Union and China, following the EU’s announcement that it plans to probe Chinese state subsidies of electric cars. European Commission Vice President Věra Jourová is also set to visit China next Monday-Tuesday and meet Vice Premier Zhang Guoqing to discuss the two sides’ technology policies, amid growing concerns over Beijing’s data gathering and cyber espionage practices.

“Alone the fine of [€345 million] is a headline sanction to impose but reflects the extent to which the DPC identified child users were exposed to risk in particular arising from TikTok’s decision at the time to default child user accounts to public settings on registration,” said Helen Dixon, the Irish data protection commissioner, in a written statement.

The Irish privacy regulator said that, in the period from July to December 2020, TikTok had unlawfully made accounts of users aged 13 to 17 public by default, effectively making it possible for anyone to watch and comment on videos they posted. The company also did not appropriately assess the risks that users under the age of 13 could gain access to its platform. It also found that TikTok is still pushing teenagers joining the platform to make their accounts and videos public through manipulative pop-ups. The regulator ordered the firm to change these misleading designs, known as dark patterns, within the next three months.

Minors’ accounts could be paired up with unverified adult accounts during the second half of 2020. The authority said the video platform had also previously failed to explain to teenagers the consequences of making their content and accounts public.

“We respectfully disagree with the decision, particularly the level of the fine imposed,” said Morgan Evans, a TikTok spokesperson. “The [Data Protection Commission]’s criticisms are focused on features and settings that were in place three years ago, and that we made changes to well before the investigation even began, such as setting all under-16 accounts to private by default.”

TikTok added it will comply with the order to change misleading designs by extending such default-privacy settings to accounts of new users aged 16 and 17 later in September. It will also roll out in the next three months changes to the pop-up young users get when they first post a video.

The decision marks the largest-ever privacy fine for TikTok, which is now actively used by 134 million Europeans monthly, and the fifth-largest fine imposed on any tech company under the GDPR.

The platform popular among teenagers has previously faced criticism for insufficiently mitigating harms it poses to its young users, including deadly viral challenges and its addictive algorithm. TikTok — like 18 other online platforms — also now has to limit risks like cyberbullying or face steep fines under the Digital Services Act (DSA).

The costly fine adds to TikTok’s woes in Europe, after it saw a wave of new restrictions on its use earlier this year due to concerns about its connection to China.

The social media app, whose parent company ByteDance is based in Beijing, has struggled to quash concerns over its data security. The company said this month it had started moving its European data to a center within the bloc. Yet, it is still under investigation by the Irish Data Protection Commission over the potentially unlawful transfer of European users’ data to China.

The Irish data authority in 2021 started probing whether TikTok was respecting children’s privacy requirements. TikTok set up its legal EU headquarters in Dublin in late 2020, meaning the Irish privacy watchdog has been the company’s supervisor for the whole bloc under the GDPR.

Other national watchdogs weighed in on the investigation over the summer via the European Data Protection Board (EDPB), after two German privacy agencies and Italy’s regulator disagreed with Ireland’s initial findings. The group instructed Ireland to sanction TikTok for nudging its users toward public accounts in its misleading pop-ups.

The board of European regulators also had “serious doubts” that TikTok’s measures to keep under-13 users off its platform were effective in the second half of 2020. The EDPB said the mechanisms “could be easily circumvented” and that TikTok was not checking ages “in a sufficiently systematic manner” for existing users. The group said, however, that it couldn’t find an infringement because of a lack of information available during their cooperation process.

The United Kingdom’s data regulator in April fined TikTok £12.7 million (€14.8 million) for letting children under 13 on its platform and using their data. The company also received a €750,000 fine in 2021 from the Dutch privacy authority for failing to protect Dutch children by not having a privacy policy in their native language.

This article has been updated.