NEW YORK -- The Justice Department is suing to block UnitedHealth Group's $3.3 billion purchase of Amedisys, citing concerns the combination would hinder access to home health and hospice services in the U.S.

The antitrust complaint , filed in Maryland by the Justice Department and four states' attorneys general Tuesday, argues that a potential merger is illegal because the two companies are "such large competitors" already — and the deal would give UnitedHealth too much control in many local markets. That would mean less choice for patients looking for affordable care, the suit alleges, as well as fewer employment options for nurses seeking competitive pay and benefits. “American healthcare is unwell," Assistant Attorney General Jonathan Kanter of the Justice Department’s antitrust division, said in a prepared statement.

“Unless this $3.3 billion transaction is stopped, UnitedHealth Group will further extend its grip to home health and hospice care, threatening seniors, their families and nurses.” Tuesday's lawsuit follows UnitedHealth's acquisition of LHC Group Inc.

, another home health and hospice provider. Since that transaction's completion last year, the Justice Department said, UnitedHealth and Amedisys have emerged as two of the largest providers of home health and hospice care in the country. The complaint alleges that UnitedHealth's plan to acquire Amedisys is the result of "an intentional, sustained strategy of acquiring, rather than beating, competition.