The High Court on Tuesday refused to hear UnitedHealth's challenge to the Center for Medicare & Medicaid Services’ (CMS) Medicare Advantage (MA) Overpayment Rule.

The Supreme Court has declined to hear UnitedHealth Group’s challenge to the 2014 MA Overpayment Rule, which required insurers to return overpayments based on incorrect diagnoses to CMS within 60 days of identifying them.

RELATED: UnitedHealth loses appeal over MA overpayments

The payer, one of the largest MA insurers in the country, sued CMS in 2016, claiming the government treated MA plans different from Medicare fee-for-service, a violation of a statute that requires equitable or the “actuarial equivalence” between CMS payments for health care coverage under MA and traditional Medicare. UnitedHealth argued that the traditional Medicare program is not subject to audits like MA plans are, which shows the MA plans are held to a higher standard than original Medicare.

In 2018, United Health scored a legal victory when a district court judge ruled that the MA overpayment rule was not equitable to Medicare and MA insurers. But last year the U.S. States Court of Appeals for the District of Columbia Circuit reversed the decision and said the overpayment rule doesn’t violate Medicare statute’s “actuarial equivalence” and “same methodology” requirements and is not arbitrary and capricious as an unexplained departure from prior policy.

In a brief filed last month, the federal government urged the Supreme Court to reject the appeal, noting that audits by the Department of Health & Human Services’ Office of Inspector General of two UnitedHealth plans found that more than 40 percent of the plans’ sampled risk scores were inaccurate due to unsupported diagnoses. The impact of the payments based on the sample was more than $500 million.

UnitedHealth told Reuters in a statement that it would continue to comply with federal rules and focus on providing high quality and affordable health care to seniors.