Washington, United States (AFP)-A US judge on Thursday ruled that Google illegally wielded monopoly power in the online ad technology market, in a legal blow that could rattle the tech giant’s revenue engine.

The federal government and more than a dozen US states filed the antitrust suit against Alphabet-owned Google, accusing it of acting illegally to dominate three sectors of digital advertising — publisher ad servers, advertiser tools, and ad exchanges.

It is one of two federal suits targeting Google that could ultimately see the company split up and curb its influence — and part of a wider government push to rein in Big Tech.

The vast majority of websites use the trio of Google ad software products that together leave no way for publishers to escape Google’s advertising technology, the plaintiffs alleged.

District Court Judge Leonie Brinkema agreed with most of that reasoning, ruling that Google built an illegal monopoly over ad software and tools used by publishers, but partially dismissed the argument related to tools used by advertisers.

“Google has willfully engaged in a series of anticompetitive acts to acquire and maintain monopoly power in the publisher ad server and ad exchange markets for open-web display advertising,” Brinkema said in her ruling.

“Google further entrenched its monopoly power by imposing anticompetitive policies on its customers and eliminating desirable product features,” she wrote.

“In addition to depriving rivals of the ability to compete, this exclusionary conduct substantially harmed Google’s publisher customers, the competitive process, and, ultimately, consumers of information on the open web.”

Google quickly vowed to appeal the ruling.

“We won half of this case and we will appeal the other half,” the company’s vice president of regulatory affairs Lee-Anne Mulholland said in a statement.

“The court found that our advertiser tools and our acquisitions, such as DoubleClick, don’t harm competition,” Mulholland said.

For Emarketer senior analyst Evelyn Mitchell-Wolf, “the bigger picture is crystal clear: the antitrust tides have turned against Google and other digital advertising giants.”

“The extent of the fallout will depend on the legal remedies employed, and the implementation timeline is likely to span years if Google loses its anticipated appeals,” Mitchell-Wolf told AFP.