My union and city have ratified a new employee contract. Included are in the retirement package is a 6nyr. DROP and a medical supplement. Employees who entered the DROP prior to the new contract are being given the option of participating in the 6th year of the DROP but are excluded from the medical supplement. Is this proper?

Proper in what context? I think it is more a matter of contract than government regulation. Depending on what the collective bargaining agreement provides, it is possibly a violation of the CBA to give existing DROP members a 6th year, with or without the medical supplement. It is possible that the CBA requires they be given that 6th year and the medical supplement.