Several prior posts have discussed California's whistleblower protection statute - Labor Code Section 1102.5.  See Court Extends California Whistleblower Protection To Third Party Violations; Can A Whistleblower Disclose What Has Already Been Reported? and Does Whistleblower Protection Extend To Disclosures To Your Mom Or The Press?  The statute prohibits retaliation against an employee for disclosing information to the government or other specified persons if "the employee has reasonable cause to believe that the information discloses a violation of state or federal statute, or a violation of or noncompliance with a local, state, or federal rule or regulation, regardless of whether disclosing the information is part of the employee’s job duties". 

In Siri v. Sutter Home Winery, Inc., Cal. Ct. App. No. A141335 (Feb. 23, 2019), the plaintiff alleged that she had been retaliated against and ultimately terminated for disclosing that her employer had failed to pay use taxes.  After failing to gain access to the employer's tax returns, the trial court granted summary judgment for the defendant.  The Court of Appeal reversed finding:

"Prosecution of plaintiff’s claim does not require the forced production of defendant’s returns or of the content of its returns.  Plaintiff’s right to recover turns only on whether she was discharged for communicating her reasonable belief that defendant was not properly reporting its use tax obligation."

The statute, however, does require "reasonable cause to believe that the information discloses a violation".  If the plaintiff does not have the information, how can she establish the requisite "reasonable cause to believe"?