TikTok was fined 530 million euros ($600 million) on Friday for violating a European Union data privacy law after regulators found the company had improperly transferred users’ personal data to China.

The Irish Data Protection Commission, which announced the penalty, said TikTok failed to adequately protect data of its users in Europe, including some that was available to staff in China, in violation of the European Union’s data privacy law, the General Data Protection Regulation.

The fine is one of the largest imposed under the law and adds to the challenges faced by TikTok’s Chinese owner, ByteDance, amid a U.S. effort to force the platform’s sale to a non-Chinese company or be banned in the United States. Irish authorities said TikTok would be ordered to suspend data transfers to China within six months if it did not meet certain requirements.