The Department of Justice has filed papers to join a lawsuit against insurance provider UnitedHealth Group over allegations that the company engaged in fraud in its Medicare Advantage plans.

The lawsuit, filed by a whistleblower in 2009, claims UnitedHealth was “gaming” the system by exaggerating patients’ conditions in order to boost its Medicare payments. Federal officials have indicated that they want to combine the case with another whistleblower suit that makes similar overpayment claims against the insurance giant.

The consolidated cases could result in damages against the company that exceed $1 billion, landing them on a list of whistleblower cases with the biggest payouts.

A spokesman for UnitedHealth said in a statement to NPR that the company denies wrongdoing, and that “litigating against Medicare Advantage plans to create new rules through the courts will not fix widely acknowledged government policy shortcomings or help Medicare Advantage members and is wrong.”