Virtual-reality startups are accusing Facebook Inc. of using a familiar playbook to muscle out rivals in what could be the digital platform of the future -- prompting a new line of scrutiny from U.S. competition enforcers.

Facebook is the world's biggest virtual-reality hardware maker thanks to its 2014 acquisition of Oculus for $2 billion. Its practices are now drawing the attention of the Justice Department's antitrust division, which is talking to developers about their interactions with the company, according to two people familiar with the matter.

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