California Code, Elections Code - ELEC § 2213

Any person may proceed by action in the superior court to compel the county elections official to cancel any registration made illegally or which should be canceled by reason of facts that have occurred subsequent to the registration.  If the voter whose registration is sought to be canceled is not a party to the action, the court may order him or her to be made a party defendant.

The county elections official and as many persons against whom there are causes of action may be joined as defendants.