DUBLIN (Reuters) - The lead European Union privacy regulator on Thursday said it had imposed a 310 million euro ($335 million) fine on Microsoft's professional networking platform LinkedIn over its targeted advertising practices.

The Irish Data Protection Commissioner (DPC) is the European Union's lead privacy regulator for most of the top U.S. internet firms due to the location of their EU operations in the country.

"The processing of personal data without an appropriate legal basis is a clear and serious violation of a data subjects' fundamental right to data protection," DPC Deputy Commissioner Graham Doyle said in a statement.

Microsoft last year said it expected to take a charge of about $425 million for a potential fine from the Irish regulator for its LinkedIn unit.

LinkedIn in a statement said: "While we believe we have been in compliance with the General Data Protection Regulation (GDPR), we are working to ensure our ad practices meet this decision by the IDPC's deadline."

($1 = 0.9260 euros)

(Writing by Conor Humphries; editing by Sarah Young)