On the heels of reports the EU was preparing to investigate Google’s ad business, the EU Commission has opened a formal investigation.

Google has been facing investigations, antitrust inquiries and lawsuits with increasing frequency. The company recently settled with the French Competition Authority over how it operates its ad platform, and committed to making significant changes.

The EU is now opening an even broader investigation, aimed at determining whether Google has used its position to favor its own ad tech services over competitors.

“Online advertising services are at the heart of how Google and publishers monetise their online services,” Executive Vice-President Margrethe Vestager, in charge of competition policy, said. “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. We are concerned that Google has made it harder for rival online advertising services to compete in the so-called ad tech stack. A level playing field is of the essence for everyone in the supply chain. Fair competition is important – 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. We will also be looking at Google’s policies on user tracking to make sure they are in line with fair competition.“

The EU’s investigation could be one of the biggest challenges the company faces, and could have profound repercussions for how it conducts its ad business. The fact that Google recently settled the French investigation, and did not dispute the facts of the case, may make it harder for the company to get ahead of the EU’s investigation.