"Res judicata prohibits relitigation of claims and issues which have already been adjudicated in an earlier proceeding." (Kelly v. Vons Companies, Inc., supra, 67 Cal.App.4th at p. 1335.) The doctrine bars a second lawsuit between the same parties on the same cause of action (claim preclusion), and it also bars a second lawsuit on matters litigated and determined in the prior proceeding (issue preclusion, also known as collateral estoppel). (Ibid.) "Issue preclusion is not limited to barring relitigation of court findings. It also 'bars the relitigation of issues which were previously resolved in an administrative hearing by an agency acting in a judicial capacity.'" (Castillo v. City of Los Angeles (2001) 92 Cal.App.4th 477, 481.) There are five requirements for issue preclusion: (1) the issue presented must be "identical" to one decided in the former proceeding; (2) the issue must have been "actually litigated" in the prior proceeding; (3) the issue must have been "necessarily decided" in the prior proceeding; (4) the decision in the prior proceeding must be final and on the merits; (5) the person subject to preclusion must have been a party to the prior proceeding or in privity with a party. (Castillo, supra, 92 Cal.App.4th at p. 481.) In Castillo v. City of Los Angeles, Castillo, a municipal employee, was dismissed for cause, due to his tardiness and unauthorized absences. Castillo appealed his discharge, and an administrative hearing was conducted. The hearing officer found that the dismissal was supported by the evidence. Castillo pursued a petition for a writ of mandate, seeking review of the administrative decision. While the petition was pending, Castillo filed an employment discrimination lawsuit, alleging that he was wrongfully terminated because of his age or national origin. After Castillo's writ petition was denied, the municipality successfully obtained summary judgment in the wrongful discharge lawsuit, on the grounds of res judicata. (Castillo, 92 Cal.App.4th supra, at pp. 479-480.) The appellate court found that the elements of issue preclusion were present, and barred Castillo's lawsuit. The relevant issue was the "wrongfulness of the discharge," which was identical in both the administrative proceeding and the wrongful termination lawsuit. (Castillo, 92 Cal.App.4th supra, at p. 481.) At the administrative level, Castillo claimed discrimination, and had ample opportunity to raise issues and present evidence to counter his employer's contention that the termination was justified. (Id. at p. 482.) Castillo argued that the issue of discrimination was not actually litigated in the administrative proceedings. The court rejected the argument, observing that the issue was addressed at the hearing, and in any event, "Castillo has not shown that he was prevented from introducing admissible evidence relevant to that issue." (Ibid.) The discrimination issue was "'necessarily decided'" because the hearing officer determined that Castillo was discharged for proper reasons: if the discharge was merely a pretext for discrimination, the officer would have found the termination inappropriate. (Ibid.) In Johnson v. City of Loma Linda (2000) 24 Cal.4th 61, a municipal employee's position was eliminated, ostensibly due to budget cuts. The employee claimed that he was terminated in retaliation for opposing sexual harassment, a claim that was rejected by the city's personnel board. The employee then sued for employment discrimination. (Johnson, supra, 24 Cal.4th at p. 66.) The Supreme Court found that the employee's discrimination lawsuit under state law "is at odds with the preceding determination by the City that the termination was for economic reasons, a finding that . . . is now binding." (Id. at p. 71.) The Court noted that government employers "provide extensive and detailed procedural protections for those challenging adverse employment actions." (Id. at p. 72.) The Court wrote, "Refusing to give binding effect to the findings of administrative agencies in quasi-judicial proceedings would . . . undermine the efficacy of such proceedings, rendering them in many cases little more than rehearsals for litigation." (Ibid.)