New York’s highest court has ruled against retired city workers who are trying to prevent Mayor Eric Adams’ administration from shifting them off of traditional Medicare, with supplemental benefits paid for by the city, and onto a private Medicare Advantage plan.

Court of Appeals Judge Shirley Troutman wrote in a unanimous decision Wednesday that retirees opposing the switch did not provide sufficient evidence to support their claim that their health coverage would be diminished under the proposed Medicare Advantage plan.

The court also ruled that the retirees did not have a legally binding promise from the city that their coverage would remain unchanged.

City Hall has argued that the switch, which would affect some 250,000 former city workers and their dependents, would save the city about $600 million a year, which could be used to pay for benefits for current city employees.

The mayor’s office did not immediately respond to a request for comment.

The Court of Appeals ruled that there are still outstanding issues in the case that must be decided by a lower court.

But the NYC Organization of Public Service Retirees, a group formed to oppose the Medicare Advantage switch, said Wednesday’s ruling effectively allows the city’s plan to move forward.

In a statement, the group said the next City Council and mayor need to "do the right thing" and codify protections for seniors in city law.

The City Council is reviewing the ruling, said Rendy Desamours, a Council spokesperson. But he added that the mayor’s office has the authority over health care decisions for municipal employees and retirees and “should bring all parties together to reach a resolution that protects adequate healthcare choices for them.”

Retirees who oppose the change in health coverage have successfully used the courts to block the switch for years. In 2021, the Court of Appeals sided with retirees who argued that the city could not require those who wanted to stay on their existing coverage to pay an extra fee. But as a result, the city eliminated that option altogether.

The Medicare Advantage switch was first announced as an agreement between former Mayor Bill de Blasio and a coalition of powerful unions representing municipal workers. But that support has since started to fracture. Michael Mulgrew, president of the United Federation of Teachers, pulled the union’s support for the plan last year, citing widespread “fear and anxiety” among retirees.

Adams has struggled to convince retirees that a custom Medicare Advantage plan designed with the insurer Aetna would not have the same issues that have been reported with some other Medicare Advantage plans, such as narrower provider networks and extra layers of approval for coverage that could delay or block care.

Although Medicare Advantage plans have become popular nationwide in recent years, in part because they often offer additional benefits, the model has also been plagued by reports of fraud and abuse that have sown skepticism.