A US judge has found that Google is illegally abusing its market dominance in online advertising technology across two markets, which could force the firm to break up some of its ad products.

The judge said that Google was guilty of “willfully acquiring and maintaining monopoly power” in its market for ad publishers and its market for ad exchanges, which acts as a middle person between buyers and sellers.

The ruling sets a pathway for Google to remedy its market dominance in these markets, which could include selling off different parts of its business, which will be determined at a subsequent trial.

The ruling follows a similar case which found that Google holds an illegal monopoly in online search.

The case found Google liable in two counts, but dismissed the third, which dealt with some of Google’s advertising tools and company acquisitions.

Publisher ad servers, which Google was found to hold an illegal monopoly over, are platforms that are used to store and manage digital ad inventory, which, when used in conjunction with ad exchanges, allows publishers to sell ads.

While consumers will not notice a major functional difference in their online ad experience due to the law, internal changes to the division of capital between advertisers, ad service providers, and publishers may result.

The ruling concurs with the UK’s Competition and Markets Authority, which found that Google’s market dominance in online advertising tech was anti-competitive.

The major anti-trust suit will be seen as a win for antitrust advocates as they look to break up large dominant companies, and challenge Google across its other dominant markets, including search.

Recommended reading

• Are Google’s Digital Advertising Methods Anti-Competitive?
• What Can We Learn From Google’s Antitrust Trials?
• Google Says Only “Harm” Will Come From Chrome Split

Google, however, contends that they will appeal the ruling and that their market practices are fair.

“We won half of this case and we will appeal the other half,” Lee-Anne Mulholland, VP of regulatory affairs at Google, said.  “Publishers have many options and they choose Google because our ad tech tools are simple, affordable and effective.”

Following the ruling, Google’s shares dropped 1.4%, though this may not be a major blow to the tech giant which still dominates search.

The Department of Justice has indicated that the ruling means Google will likely have to sell its Google Ad Manager to appease the decision, which would include its ad exchange and publisher ad server.