1, There are explicit exemptions for government retirement plans in ERISA. I'm not an expert, but surface level research says that state/local government plans have more leeway in accounting and reporting practices and are not insured by the pension benefit guaranty corporation.

2, central to the point of this is that the union leadership is telling members to encourage their representatives to change the law to allow for reduced benefits. Even if there are ERISA protections from members now the union leadership is attempting to remove them in the future.