The U.S. Justice Department and four states sued Tuesday to block UnitedHealth Group's proposed $3.3 billion acquisition of Amedisys, a Louisiana-based home health company that would further United's push into the home care and hospice markets.

The complaint marks the second time in less than three years that the DOJ has tried to stop Minnetonka-based UnitedHealth from completing deals to bolster its fast-growing Optum division for health care services, which complement the company's legacy health insurance business. The government unsuccessfully sued to block Optum's acquisition of Change Healthcare in 2022.

In the new case, the government alleges the acquisition of Amedisys would harm competition because UnitedHealth previously completed a $5.4 billion acquisition of LHC Group, another home care and hospice company based in Louisiana. United's LHC Group and Amedisys are two of the three largest home health and hospice providers in the country, according to the DOJ.

The lawsuit also echoes questioning from some in Congress earlier this year about whether UnitedHealth Group has gotten too big, particularly as it provides more care directly to patients.

"Beyond the markets at issue here, this merger would also affect American health care more broadly," the complaint states. "This merger would also further UnitedHealth's standing as the dominant force in nearly every corner of the American health care system. Over the past three years, UnitedHealth has spent more than $36 billion acquiring companies in a variety of health care settings."

UnitedHealth Group runs UnitedHealthcare, which is the nation's largest health insurer, as well as Optum, which manages pharmacy benefits, outpatient medical centers, medical billing and health care data analytics for millions of patients across the country.

In U.S. metropolitan areas with about 500,000 residents, an average of 26 home health agencies serve each metro area, UnitedHealth said on a website it launched Tuesday to defend the acquisition. The numbers illustrate the "highly fragmented nature" of the industry, the company says, and the large number of options available to patients. With the acquisition, UnitedHealth would operate "just a fraction of all home health and hospice care centers nationally."

In a statement, the health care giant said the "Amedisys combination with Optum would be pro-competitive and further innovation, leading to improved patient outcomes and greater access to quality care. We will vigorously defend against the DOJ's overreaching interpretation of the antitrust laws."

The DOJ filed the lawsuit in U.S. District Court in Maryland, with four states as co-plaintiffs: Illinois, Maryland, New Jersey and New York.

It alleges the acquisition would let UnitedHealth expand its home health and hospice operations to an additional five states while gaining nearly 500 locations across 32 states where it already competes. As result, the company would control of 30% or more of the home health or hospice services in eight states, according to the lawsuit.

The merger would give UnitedHealth Group too much power, the government argues, not just in a sector that patients rely on for critical services, but also in the labor market for home care nurses. The complaint identifies dozens of local home health, hospice and labor markets across the country — none in Minnesota — where the acquisition would result in "presumptively unlawful" concentrations.

UnitedHealth has proposed addressing competitive concerns, the DOJ said, through a divestiture of certain facilities to another company that operates in the market. The government's complaint, however, questioned whether this third-party would be a viable competitor, while stressing it would "not resolve the competitive overlap in over 100 home health and hospital markets across 19 states and the District of Columbia."

"We are challenging this merger because home health and hospice patients and their families experiencing some of the most difficult moments of their lives deserve affordable, high quality care options," U.S. Attorney General Merrick Garland said in a news release Tuesday. "The Justice Department will not hesitate to check unlawful consolidation and monopolization in the health care market that threatens to harm vulnerable patients, their families and health care workers."

In February 2022, the Justice Department filed a lawsuit to block UnitedHealth's $13 billion acquisition of Tennessee-based medical billing clearinghouse Change Healthcare, a bigger deal that the federal government said could potentially harm millions of Americans by lowering the quality of health insurance while making coverage more costly.

The judge ruled that the DOJ didn't convincingly prove the company would misuse Change Healthcare's data to promote its own health insurance business or raise rivals' costs and limit innovation.

Following a large-scale data breach earlier this year at Change, UnitedHealth Group CEO Andrew Witty was called to testify in May before two congressional committees. In the Senate, questions about the company's size came from lawmakers including Sen. Elizabeth Warren, D-Mass., who asserted UnitedHealth Group is a "monopoly on steroids."

Witty testified his company owns no hospitals or drug manufacturers — two key health care sectors — and works with most of its 90,000 affiliated physicians on a contract basis, rather than via outright ownership arrangements.

Earlier this year, the Wall Street Journal cited unnamed sources saying the DOJ had opened an antitrust investigation related to UnitedHealth's acquisition of medical groups across the country.

In the new lawsuit, the DOJ says Amedisys and LHC Group, the other home care firm acquired by UnitedHealth, were two of the three largest competitors in a market where the third big player is owned by Kentucky-based Humana, another large health insurer. The Justice Department says home health services are used predominantly by patients insured via Medicare, including privately run Medicare Advantage programs.

"If UnitedHealth succeeds in buying one of its most significant competitors in these presumptively anti-competitive markets, the nation's three largest home health providers would be owned by the nation's two largest Medicare Advantage insurers," the lawsuit says.

Before LHC Group was acquired by United, the company's nurses and health professionals made about 12 million visits to patients in 32 states and the District of Columbia, the DOJ says, generating more than $2.3 billion in revenue. Last year, Amedisys caregivers made 10.6 million visits to patients in 37 states and the District of Columbia, the government says, delivering revenue of $2.2 billion.

"UnitedHealth's acquisition of Amedisys would ensure that UnitedHealth, not competition, would determine outcomes for patients in home health and hospice and for the nurses that provide services in hundreds of local markets across the country," the complaint says.