The U.S. Department of Justice (DOJ) is again involved in a lawsuit alleging UnitedHealth Group (UHG) received Medicare Advantage payments to which it wasn’t entitled.

In this case, DOJ said UnitedHealth, the largest Medicare Advantage insurer, has collected more than $1 billion since 2005 through a national effort to identify additional diagnoses and increase a patient’s risk adjustment payment from CMS.

“However, UHG allegedly ignored information from these chart reviews showing that hundreds of thousands of diagnoses provided by treating physicians and submitted by it to Medicare were invalid and did not support the Medicare payments it had previously requested and obtained. By ignoring this information, UHG avoided repaying Medicare monies to which it was not entitled,” DOJ said in a press release.

The suit also alleged UHG ignored invalid diagnoses from providers which had a strong financial incentive to help the insurer increase Medicare Advantage payments, which would also benefit the providers.

The complaint was originally brought to court former UnitedHealth executive-turned-whistleblower Benjamin Poehling, who told the New York Times the search for additional diagnoses was “all about the bottom line,” not improving patient outcomes.

DOJ had already sought to intervene in a related whistleblower case against UHG, and Kaiser Health News reported in March the department planned on consolidating the two lawsuits.

The insurer has continued to deny the allegations.

“We are confident our company and our employees complied with the government's Medicare Advantage program rules, and we have been transparent with CMS about our approach under its unclear policies," UHG spokesperson Matt Burns said in a statement.