BRUSSELS — The European Union on Friday said Meta and TitTok had breached their transparency obligations after an investigation that could result in billions of dollars in fines.

The inquiry found both companies had violated the Digital Services Act , the EU’s trailblazing digital rule book that imposes a set of strict requirements designed to keep internet users safe online, including making it easier to report counterfeit or unsafe goods or flag harmful or illegal content like hate speech, as well as a ban on ads targeted at children.

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