California Code, Code of Civil Procedure - CCP § 391.1

(a) In any litigation pending in any court of this state, at any time until final judgment is entered, a defendant may move the court, upon notice and hearing, for an order requiring the plaintiff to furnish security or for an order dismissing the litigation pursuant to subdivision (b) of Section 391.3. The motion for an order requiring the plaintiff to furnish security shall be based upon the ground, and supported by a showing, that the plaintiff is a vexatious litigant and that there is not a reasonable probability that they will prevail in the litigation against the moving defendant.

(b) A motion pursuant to subdivision (a) on the grounds that plaintiff is a vexatious litigant pursuant to paragraph (5) of subdivision (b) of Section 391 may be brought only by a person protected by the restraining order. A person filing a motion as described in this subdivision shall not be required to pay a filing fee.