According to the unions, the unilateral change raised rates another 2 percent for retirees who were contributing 10 percent of individual premiums and 25 percent for family coverage based on contracts when they retired.
The unions are the Civil Service Employees Association, Public Employees Federation, United University Professions, State Correctional Officers and Police Benevolent Association, the State Troopers Police Benevolent Association, State Police Investigators Association and AFSCME Council 82.
They say they represent most of the state's more than 250,000 workers.
A Cuomo spokesman says the law allows the administration to apply new contract terms to retirees and that has been standard practice.