Facebook owner Meta Platforms must face trial in a U.S. Federal Trade Commission lawsuit seeking its break up over claims that it bought Instagram and WhatsApp to crush emerging competition in social media, a judge in Washington ruled on Wednesday.

Judge James Boasberg largely denied Meta's motion to end the case filed against Facebook in 2020, during the Trump administration, alleging that the company acted illegally to maintain its social network monopoly.

Meta, then known as Facebook, overpaid for Instagram in 2012 and WhatsApp in 2014 to eliminate nascent threats instead of competing on its own in the mobile ecosystem, the FTC claimed.

Boasberg let that claim stand, but dismissed the FTC's allegation that Facebook restricted third-party app developers' access to the platform unless they agreed not to compete with its core services.

The judge also disallowed Meta from raising as a defense that the WhatsApp acquisition benefited its strategic position towards Apple and Google. The judge said he would release a detailed ruling later on Wednesday after the FTC and Meta have had a chance to redact any sensitive commercial information.

A trial date in the case has not been set.

Meta had urged the judge to dismiss the entire case, saying it depended on an overly narrow view of social media markets, and did not take into account competition from ByteDance's TikTok, Google's YouTube, X, and Microsoft's LinkedIn.

The case is one of five blockbuster lawsuits where antitrust regulators at the FTC and U.S. Department of Justice are going after Big Tech.

Amazon.com Inc. and Apple are both being sued, and Alphabet's Google is facing two lawsuits, including one where a judge recently found it unlawfully thwarted competition among online search engines.