US regulator has filed a civil lawsuit to block UnitedHealth Group’s $13bn acquisition of Change Healthcare.

The lawsuit filed by the Department of Justice, together with Attorneys General in Minnesota and New York, argues that the deal would harm competition in the commercial health insurance market.

It will also impact the market for technology used by health insurance firms to process claims and reduce costs, the regulator said.

In January 2021, United announced plans to buy healthcare technology provider Change via Optum.

38 of the 40 leading health insurers in the US use Change’s and United’s first-pass claims editing solutions and if the deal materialises, the firms will collectively control nearly 75% of the market, the DOJ said in its complaint.

The regulator alleged that United understands that through the acquisition, it will be able to access the proprietary plan and payment rules of rival health insurers such as Humana, Anthem, CVS Health Corp’s Aetna and Cigna.

DOJ Antitrust Division Principal Deputy Assistant Attorney General Doha Mekki said: “The proposed transaction threatens an inflexion point in the health care industry by giving United control of a critical data highway through which about half of all Americans’ health insurance claims pass each year.

“Unless the deal is blocked, United stands to see and potentially use its health insurance rivals’ competitively sensitive information for its own business purposes and control these competitors’ access to innovations in vital health care technology.”

Responding to the lawsuit, UnitedHealth said it would appeal against it. “The Department’s deeply flawed position is based on highly speculative theories that do not reflect the realities of the healthcare system. We will defend our case vigorously,” it said in a statement.