California Code, Elections Code - ELEC § 2142

(a) If the county elections official refuses to register a qualified elector in the county, the elector may proceed by action in the superior court to compel his or her registration. In an action under this section, as many persons may join as plaintiffs as have causes of action.

(b) If the county elections official has not registered a qualified elector who claims to have registered to vote through the Department of Motor Vehicles or any other public agency designated as a voter registration agency pursuant to the federal National Voter Registration Act of 1993 (52 U.S.C. Sec. 20501 et seq.), the elector may proceed by action in the superior court to compel his or her registration. In an action under this section, as many persons may join as plaintiffs as have causes of action.

(c) No fee shall be charged by the clerk of the court for services rendered in an action under this section.