No California court has yet determined the rights of an employee under the circumstances you describe here.
Were I representing you in court, I would use the following argument to protect your rights:
- The "analytical framework" for assessing privacy claims should proceed as follows: "First, the claimant must possess a `legally protected  privacy interest.' [Citation.] An apt example from Hill [v. National Collegiate Athletic Assn. (1994) 7 Cal.4th 1 [26 Cal.Rptr.2d 834, 865 P.2d 633]] is an interest `in precluding the dissemination or misuse of sensitive and confidential information ("informational privacy") ....' [Citation.] Under Hill, this class of information is deemed private `when well-established social norms recognize the need to maximize individual control over its dissemination and use to prevent unjustified embarrassment or indignity.' [Citation.] ... [¶] Second, Hill teaches that the privacy claimant must possess a reasonable expectation of privacy under the particular circumstances, including `customs, practices, and physical settings surrounding particular activities ....' [Citation.] As Hill explains, `A "reasonable" expectation of privacy is an objective entitlement founded on broadly based and widely accepted community norms.' [Citation.] `[O]pportunities to consent voluntarily to activities impacting privacy interests obviously affect the expectations of the participant.' [Citation.] [¶] Third, Hill explains that the invasion of privacy complained of must be `serious' in nature, scope, and actual or potential impact to constitute an `egregious' breach of social norms .... [¶] Assuming that a claimant has met the foregoing Hill criteria for invasion of a privacy interest, that interest must be measured against other competing or countervailing interests in a `"balancing test."' [Citations.] (7) `Conduct alleged to be an invasion of privacy is to be evaluated based on the extent to which it furthers legitimate and important competing interests.' [Citation.] Protective measures, safeguards and other alternatives may minimize the privacy intrusion. `For example, if intrusion is limited and confidential information is carefully shielded from disclosure except to those who have a legitimate need to know, privacy concerns are assuaged.'" (Pioneer Electronics, supra, 40 Cal.4th at pp. 370-371.)
Based upon the above, my argument would be that even as an employee, you are entitled to privacy in allegations of wrongful acts done by you in the workplace, because the common law provides that such invasions which cast a person in a false light towards others is actionable -- and that there is no special immunity provided to employers.
The disclosure of the complaints against you to the other employees was an outrageous invasion of your privacy rights, and to the extent that it deters your ability to perform your job functions, the disclosure should be actionable in the event that you are later terminated for being unable to continue to perform as manager.
The question of whether or not you can immediately sue your employer for the disclosure is more difficult. That is, the legal claim of "false light attribution" is a viable lawsuit. But, if you were to immediately sue, then the collateral issue of whether or not your employer could terminate you for doing so, becomes an issue -- at which point, my original argument that your termination would actually be caused by the employer's invasion of your privacy rights, and so the courts should prohibit the termination.
This is an extraordinarily complicated legal cause of action. I realize that you are looking for some simple statement of law, such as a section of the California Labor Code, which would immediately protect your interests. However, no such straightforward law exists. My argument here would be the best that you could do.
In sum, you may want to consider trying to negotiate some sort of resolution of the matter with your employer. If you cannot do so, then you could shop your case facts to 3-4 employment rights attorneys and see if anyone is interested in a novel lawsuit, such as you allegations appear to suggest.
That's really the best that anyone can do in this situation, because the state legislature has simply not provided any direct means of holding your employer liable for the unauthorized disclosure of of the sort of confidential information you describe.
To be sure, there is a colorable legal action here. But, finding a lawyer to "take the case" is a different question -- because, as there is no certainty in the outcome, you need a lawyer willing to take a risk -- and that can be a difficult thing to find.
This is some very difficult subject matter. If my answer is difficult to understand, feel free to ask for clarification and I will be happy to try to speak more plainly.
Hope this helps.