LONDON (AP) — European Union regulators have launched a fresh antitrust investigation of Google, this time over whether the U.S. tech giant is stifling competition in digital advertising technology.

The EU's executive Commission said Tuesday that it has opened a formal investigation into whether Google violated the bloc's competition rules by favoring its own online display advertising technology services at the expense of rival publishers, advertisers and advertising technology services.

The commission said it's looking in particular at whether Google is restricting access by third parties to user data for ad purposes on website and apps.