In nearly every case in which employment discrimination or retaliation is alleged, one question can be pivotal: Did the employer genuinely believe it had legitimate reasons for the challenged decision or conduct? Although a successful defense hinges on the existence of a business-related reason that is unrelated to a prohibited motive, an employer need not prove that its decision was wise or correct as a matter of objective proof. (See Harris v. City of Santa Monica, 56 Cal. 4th 203 (2013).) However, earlier this year the court of appeal appended an important caveat to this settled rule, making clear that the employer's decision-making process must include an adequate investigation of the facts, especially if there are conflicting versions of what happened. (See Mendoza v. W. Med. Ctr. Santa Ana, 222 Cal. App. 4th 1334 (2014).) In the Mendoza case, the plaintiff was an excellent employee who complained that his supervisor sexually harassed him. The employer investigated, but it did not promptly interview the alleged harasser, nor request that either he or the plaintiff provide a written statement. Instead, after suspending the investigation for several weeks for a reason unrelated to the complaint, another supervisor jointly interviewed the plaintiff and the alleged harasser. The employer did not interview anyone else, even though there were starkly different explanations for what may have occurred. In the end, the employer essentially threw up its hands and terminated both the plaintiff and the alleged harasser on the grounds both had committed misconduct. (Mendoza, 222 Cal. App. 4th at 1337.) The plaintiff sued for wrongful termination in violation of public policy, alleging the employer had retaliated against him for complaining about harassment. The plaintiff's expert criticized the employer's investigation, emphasizing: the lack of a formal investigation plan; the absence of written statements; the failure to immediately interview the alleged harasser; the simultaneous interview of the alleged harasser and the plaintiff; the failure to interview others who might have provided helpful information; and the fact that the investigator was not a trained HR professional. (See Mendoza, 222 Cal. App. 4th at 1344.) At trial, the jury found the employer liable for wrongful termination. Although the court of appeal reversed and remanded for a new trial because of an erroneous jury instruction on causation, the opinion in Mendoza emphasized that there was at least an inference that the employer did not value the truth, but sought rather "to clean up the mess that was uncovered when [the plaintiff] made his complaint." (Mendoza, 222 Cal. App. 4th at 1344.) The court bluntly rejected the employer's argument that it reasonably terminated both employees because it was faced with "a scenario in which two employees provide conflicting accounts of inappropriate conduct." Highlighting the employer's obligation to "conduct a thorough investigation and make a good faith decision based on the results of the investigation," the court stated its decision should "disabuse employers of the notion that liability (or a jury trial) can be avoided simply by firing every employee involved in the dispute." (Mendoza, 222 Cal. App. 4th at 1345 n.4.) Given its somewhat unusual facts, the reach of Mendoza's holding should be confined to cases in which the employer terminates (or disciplines) an employee after conducting an investigation that is insufficient to support a good faith decision about what may have occurred. But if the employer does conduct a reasonable investigation and relies on the results, it may still be possible to obtain summary judgment and defend the decision-making process on appeal. When responding to employee complaints, best practices suggest that the employer should document its prompt action upon receiving a complaint; that it utilized a qualified investigator; and that it identified and interviewed persons who might have relevant information. In addition, when faced with conflicting accounts about what occurred, employers should document the reasons for believing one employee instead of another. These steps offer protection should the employer later be called upon to defend its decision-making process in court or arbitration. M. Michael Cole is an associate at Miller Law Group, a management-side employment law firm with offices in San Francisco and Los Angeles.