(Bloomberg) -- The US Department of Justice has initiated an antitrust investigation into UnitedHealth Group Inc., people familiar with the matter said Tuesday.

The probe opens a new layer of scrutiny on the largest US health insurer that operates in pharmacy benefits, medical care, technology and other services. It emerged out of concerns about UnitedHealth’s acquisitions of health-care providers and data companies, according to one of the people, who asked not to be identified discussing information that isn’t public. 

The company and the Justice Department both declined to comment. UnitedHealth shares dropped as much as 5% at the New York market open Wednesday, the most intraday in a month.

UnitedHealth has drawn criticism for years as it has expanded its reach across the health-care system. Best known for its UnitedHealthcare insurance unit that covers more than 47 million Americans, it gets a growing share of revenue and profits from health-services businesses under its Optum arm.

Optum’s clinics, home-care services, drug plans and pharmacies frequently provide services to UnitedHealthcare members, allowing the company to turn expenses in its insurance business into revenue for Optum. That arrangement has helped power UnitedHealth’s growth, a strategy that competitors have attempted to replicate. 

Regulatory Scrutiny

But it has also drawn criticism from antitrust regulators. The Justice Department is also reviewing UnitedHealth’s planned $3.3 billion purchase of home-health provider Amedisys Inc. after the acquisition of rival LHC Group last year. The department sued unsuccessfully to block the health-care giant from acquiring Change Healthcare — the largest electronic data clearinghouse that connects doctors, hospitals, dentists and pharmacies with insurance companies to obtain reimbursement — in 2022. 

Read More: Fallout from Change Healthcare Hack Still Roiling Health Care

UnitedHealth executives have said the company enforces strict separation between its insurance business and its Optum services and emphasizes that Optum sells to many other insurance companies that compete with UnitedHealthcare.

A local news outlet in New York, the Examiner News, reported on Monday that UnitedHealth faced the antitrust probe. The Wall Street Journal reported the investigation Tuesday.

The Examiner News, which has reported on Optum’s acquisition of clinics north of New York City, cited internal company emails saying the company received notice of the investigation in October. 

UnitedHealth is subject to investigations, audits or reviews by more than a dozen US authorities, including the Department of Justice, according to the company’s regulatory filings.

(Updates with opening share move in third pargraph)

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