Legal Question in Business Law in California

Contracts against competion by former employees are generally not enforceable in Calif.

Although Mr. Marman is correct, your situation appears to be different. In order to get a "temporary cease and desist order" (i.e. injunction or restraining order) you will need to file suit against the partner. You do not provide enough facts to determine whether this is a viable option. You will need to review your partnership agreement (or better have an attorney review it) to determine whether the partner is violating it. If this is the case you should start by sending a cease and desist letter to the partner. A letter from your attorney would probably carry more weight. Having an attorney involved from the beginning will benefit you in the long run.