Apple's main regulator in the European Union, the Irish Data Protection Commissioner (DPC), has opened a third privacy investigation into the iPhone maker over the last few weeks, a spokesman for the DPC said.

The probe is examining whether Apple has complied with the relevant provisions of the EU's new General Data Protection Regulation (GDPR) privacy law in relation to an access request from a customer.

It follows investigations opened last year regarding how Apple processes personal data for targeted advertising on its platform and whether its privacy policy on the processing of that data is sufficiently transparent.

The Data Protection Commission has 20 investigations open into multinational technology companies whose European headquarters in Ireland puts them under its watch, with Facebook under the most scrutiny with eight individual probes, plus two into its WhatsApp subsidiary and one into Facebook-owned Instagram.

Like Apple, Twitter is also under three different investigations with one each for Google, Microsoft-owned LinkedIn and US digital advertising company Quantcast.

Under GDPR, regulators have the power to impose fines for violations of up to 4% of a company's global revenue or €20 million, whichever is higher.