LONDON (AP) — European Union regulators slapped LinkedIn on Thursday with a 310 million euro ($335 million) fine for violations of the bloc's stringent data privacy rules.

Ireland's Data Protection Commission reprimanded the Microsoft-owned professional social networking site over concerns about the “lawfulness, fairness and transparency” of its personal data processing for advertising purposes.

The Dublin-based watchdog is LinkedIn's lead privacy regulator in the 27-nation EU because that's where the company's European headquarters is based.

The watchdog said it carried out an investigation that found LinkedIn did not have a lawful basis to gather data so it could target users with online ads, which is a breach of the privacy rules known as General Data Protection Regulation, or GDPR. It ordered LinkedIn to comply with the rules.

Processing personal data “without an appropriate legal basis is a clear and serious violation” of the right to data protection in the EU, Deputy Commissioner Graham Doyle said in a statement.

LinkedIn said it that while it believes it has been “in compliance” with the rules, it's working to ensure its “ad practices” meet the requirements.