Judges are expected to issue their ruling in the Google antitrust case next year, which can be appealed to the Court of Justice, Europe's highest.
Mac Eochaidh repeatedly asked Google what it had refused to supply to its competitors
Google's battle against a $2.6 billion EU antitrust fine was dealt an apparent setback on Thursday, when one of the judges hearing the case said the company had committed a "clear infraction" in its handling of price-comparison shopping services.
The comments by Colm Mac Eochaidh, one of the panel of five judges, came on day two of a three-day hearing at Europe's General Court - its second highest - as Google seeks to overturn the first of a trio of EU antitrust penalties.
In its 2017 decision to impose a EUR 2.4-billion ($2.6 billion) fine, the European Commission said the world's biggest Internet search engine unfairly favoured its own price-comparison shopping service over smaller European rivals.
Irish judge Mac Eochaidh concurred.
"For me, this case really is visibility. This is a very important point in the case. It is perfectly apparent what has happened is this: you have promoted your own service and demoted that of others," he said. "That is a clear infraction."
Mac Eochaidh repeatedly asked Google what it had refused to supply to its competitors that had forced them to air their grievances to EU enforcers.
Google's lawyer Christopher Thomas faulted the Commission for not taking Amazon into account when defining the market for assessing the competitive harm caused by Google's practices.
Regulators were right to discount Amazon's role, said Thomas Hoppner, lawyer for several German complainants.
"Merchant platforms and CSSs (comparison shopping services) simply cater to different needs of different types of online retailers. These different needs mean that CSSs cannot easily be transformed into merchant platforms and vice versa," he said.
"The entire Google story that the condemned conduct was a means to compete with Amazon has no merits."
Judges are expected to issue their ruling next year, which can be appealed to the Court of Justice, Europe's highest.
The case is T-612/17 Google and Alphabet v Commission.
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