How have courts dealt with claims that an employer fired an employee for breaching internal policy?

Analogous claims were made by the plaintiff in Burton v. Security Pacific Nat. Bank (1988) 197 Cal.App.3d 972, 243 Cal.Rptr. 277, where the appellate court affirmed a summary judgment in favor of the defendant employer. The employee had been fired for reading confidential materials kept in a restricted area. He denied the accusation, claiming he had been reading nonconfidential material in an open area. The employee alleged the reason given by the employer for his termination was untrue and used as a pretext; the employer actually wanted to get rid of him before he filed a grievance for the employer's prior violation of internal policy. But the employee had no material facts to support the pretext theory, and undisputed facts showed the employer had investigated the charge before terminating him.