The European Union announced that it is investigating whether Google’s advertising business has violated EU competition rules.

“Online advertising services are at the heart of how Google and publishers monetize [its] online services,” European Commission executive vice president Margrethe Vestager says of the investigation. “Google collects data to be used for targeted advertising purposes, it sells advertising space and also acts as an online advertising intermediary. So Google is present at almost all levels of the supply chain for online display advertising.”

As Ms. Vestager explains it, the Commission is concerned, understandably, that Google destroys competition in the online advertising market that it now dominates. “Fair competition is important: she notes, “both for advertisers to reach consumers on publishers’ sites and for publishers to sell their space to advertisers, to generate revenues and funding for content.” As a result, the EC is examining Google’s user tracking policies to ensure that they do not harm competition.

The primary concern, apparently, is whether Google harms competition by restricting access to user data for advertising purposes on websites and apps for third parties while keeping that data to itself for use in its own services. The EU estimates that this market is currently worth $24 billion annually, and is growing rapidly.