The ruling by District Judge Beth Labson Freeman in San Jose, California, marks one of the first major decisions in a spate of antitrust cases filed against Google over the last two years by users and rivals as well as the U.S. Department of Justice and state attorneys general.
Labson Freeman said plaintiffs, including Hanson Law Firm and Prana Pets, that alleged Google abuses its dominance in digital advertising need to clarify which market they think it monopolizes.
"The Court is particularly concerned that Plaintiffs' market excludes social media display advertising and direct negotiations," she wrote.
The plaintiffs also need to better explain why Google's refusal to support rival systems that the advertisers rely upon is anticompetitive, because antitrust law does not require monopolists to help competitors survive, Labson Freeman said.
"The Court has serious concerns that some of Plaintiffs' allegations rely on a 'duty to deal' theory of antitrust," she wrote.
Plaintiffs have until June 14 to amend their lawsuit, according to the decision.
Attorneys for Google and the plaintiffs did not immediately respond to requests for comment.
Google in other cases faces claims about its dominance of search and mobile software businesses. InItial decisions in those cases could be years away. For instance, a federal judge in Texas this month heard arguments on whether to schedule a trial for the spring of 2022, as states that brought the lawsuit prefer, or fall of 2023, as Google seeks.
(Reporting by Paresh Dave; editing by Jane Wardell and Leslie Adler)
By Paresh Dave