Signing an additional "contract"

I have a contract with my employer through my union's collective bargaining agreement. It basically spells out what rights I have and the rights of the hospital. The management in my unit has recently asked me to sign an additional "contract" for us to agree to do certain things (ie. I will come to work on time, I will be in proper uniform ect). Aren't these things covered under my general employment contract? My current contract doesn't say I have to sign any additional contracts and there is no hospital policy stating that we must do so. Although I think this is more symbolic in nature and I already follow all the rules and procedures of the hospital, I don't want to sign it. Could the hospital impose disciplinary action against me for not signing this thing?