(Bloomberg) -- Meta Platforms Inc. was hit with a €798 million ($841 million) fine by European Union regulators by tying its Facebook Marketplace service to the social network, the US tech giant’s first ever penalty for EU antitrust violations.

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In a groundbreaking decision, the European Commission ordered Meta to stop tying its classified-ads service to Facebook’s sprawling social media platform, and refrain from imposing unfair trading conditions on rival second-hand goods platforms.

“Meta tied its online classified ads service Facebook Marketplace to its personal social network Facebook and imposed unfair trading conditions on other online classified ads service providers,” EU antitrust chief, Margrethe Vestager, said. “It did so to benefit its own service Facebook Marketplace.”

The move adds to a spate of bad news for Meta. A US judge ruled that the Federal Trade Commission’s antitrust lawsuit against the company can continue to trial on Wednesday, while Donald Trump was elected US president again. His victory helped propel the social networking app Bluesky, which competes with Meta’s Threads, to the top of Apple Inc.’s US App Store.

Trump called Facebook an “enemy of the people” just eight months ago and suggested Chief Executive Officer Mark Zuckerberg should go to jail.

The EU fine is likely to be one of the final acts for Vestager, who’s set to leave her post before the end of the year. Over the past decade, she has been one of Silicon Valley’s toughest critics levying billions of euros in antitrust penalties, including over €8 billion in fines against Google.

The decision follows a probe into how Meta leverages Facebook’s billions of users to squeeze out rivals. EU watchdogs said Menlo Park California-based Meta also used data from rival platforms that advertised on Facebook to boost its Marketplace service.

Meta vowed to appeal the decision at the bloc’s courts, a process that could take several years. It said the penalty “ignores the realities of the thriving European market” and “shields large incumbent companies.”

Meta shares fell as much as 1% after trading opened in New York. The company was earlier fined €110 million by the EU merger regulator for providing misleading information about its takeover of messaging service WhatsApp in 2017.