The European Union just fined Google $2.7 billion. And that might not even be the worst news for Mountain View.

Today the EU's executive branch, the European Commission, also ordered Google to change the way it displays search results from its online shopping tool. When you search for a product, Google has long shown results from Google Shopping in a box that floats above its regular search results. The commission ruled that this preferential treatment of its own content is illegal and anti-competitive. The company has 90 days to begin ranking its own shopping comparison in the same way it lists those from competitors, or face additional fines of up to five percent of its average annual turnover. The order only applies to search results in the European Union.

The big issue for Google isn't necessarily the fine, or even the change to its shopping listings. It's the fact that regulators are forcing it to change how it handles search. The company has been retooling its search results to be more than just a list of websites. As Google expands into new areas, such as voice-controlled virtual assistants, it seeks to provide people with what they're looking for directly, whether that's an answer to a question, the address of a restaurant, or a list of nearby movie showings. Today's order chips away at that idea by opening the door to more lawsuits.

That's good news for competing shopping sites, which can now also sue Google in European civil court, and potentially for other companies as well. Yelp has long complained about the way Google lists its own restaurant reviews over those of competitors, and today's decision could be the first step towards changing that.

Since Google can still appeal the case, it's still too early for those competitors to celebrate, though some hope it's a signal of changes to come. "This will be the most significant enforcement event in consumer tech antitrust in nearly 20 years," Yelp VP of policy Luther Lowe wrote on Twitter yesterday, citing the Justice Department's landmark ruling against Microsoft in 2000 as the last major event in tech antitrust history. But the potential impact is still far from certain.

The Case Against (and For) Google

Today's order was a long time coming. The EU began its investigation in 2010, after British price comparison site Foundem, French legal search engine eJustice.fr, and Microsoft-owned Ciao from Bing complained that Google's practices put competitors at a disadvantage. But the regulators didn't formally accuse the Google of an antitrust violation until 2015.

The commission analyzed the results of 1.7 billion real Google search queries—around 5.2 terabytes of data—and concluded that, on average, the company placed results from competing online shopping services only on the fourth page of its results.

"Google has come up with many innovative products and services that have made a difference to our lives," EU Commissioner Margrethe Vestager said in a statement today. "That's a good thing. But Google's strategy for its comparison shopping service wasn't just about attracting customers by making its product better than those of its rivals. Instead, Google abused its market dominance as a search engine by promoting its own comparison shopping service in its search results, and demoting those of competitors."

Barry Lynn, author of Cornered: The New Monopoly Capitalism and the Economics of Destruction and the head of the New America Foundation's Open Markets program, compares Google's behavior to a railroad that steers its riders to stores that the railroad company also owns.

But Google has long argued that online shopping is more competitive than ever and that Amazon and eBay, not Google, are the truly dominant players in the market.