The Justice Department and two states appealed a federal judge’s decision to toss a challenge to UnitedHealth Group’s $13 billion merger with technology company Change Healthcare, according to a court notice filed Friday.

The federal government, New York and Minnesota did not specify why they were appealing Judge Carl Nichols’ ruling, which he handed down in the US District Court for the District of Columbia in September.

The Justice Department sued to block the deal in February, alleging it would violate federal antitrust law by giving insurer UnitedHealthcare access to intelligence on how rival health insurance companies structure their provider networks. The plaintiffs waited until the final possible day to appeal Nichols’ decision. The Justice Department now faces the challenge of potentially breaking up a combined company.

UnitedHealth Group completed its $13 billion merger with Change Healthcare in October. UnitedHealth Group paid $7.8 billion in cash and assumed $5 billion in debt to acquire Change Healthcare, and incorporated its operations into the fast-growing OptumInsight revenue cycle management division. The company also sold Change Healthcare’s claims processing service to a private equity firm for $2.2 billion last month.

UnitedHealth Group, Change Healthcare and the Justice Department did not immediately respond to interview requests.