The Federal Trade Commission is investigating Amazon’s $3.9 billion acquisition of the primary health organization One Medical, a move that could delay the completion of the deal.

Both One Medical and Amazon received a request for additional information Friday in connection with an FTC review of the merger, according to a filing made with securities regulators by One Medical’s parent, San Francisco-based 1Life Healthcare Inc.

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Groups calling for stricter antitrust regulations have urged the FTC to block the One Medical merger, arguing it would further expand Amazon’s massive market power. When it was announced in July, the American Economic Liberties Project in Washington said it was unclear if Amazon would protect patients and their sensitive medical records.

“Allowing Amazon to control the health care data for another 700,000 plus individuals is terrifying,” Krista Brown, the group’s senior policy analyst, said in a July statement. “Amazon has no business being a major player in the healthcare space, and regulators should block this $4 billion deal to ensure it does not become one.”

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