Cal. Civ. Proc. Code § 391.1

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. The motion must 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 he will prevail in the litigation against the moving defendant.