My psychologist is referring me for a mental health assessment saying i'm medication non compliant and my depression needs assessment. is this something i can say no to? or is it involuntary?

Depends: In the US a person who is considered an adult under prevailing law (local issue) can agree to or refuse care. If the person is a minor or the assessments are part of court ordered evaluations they can proceed with or without your permission. When you post on this site the more detailed information you provide the more likely we can provide an adequate answer in the limited space allowed.

Mental Health Eval: I live & work in the United States, so I am not familiary with legal aspects of psychiatry in Australis. In the United States, a simple medical referral is voluntary. Sometimes the court system my become involved if you are a danger to your self or others, can no longer care for yourself or have lost touch with reality.