In California, employees who blow the whistle are protected from retaliation by Labor Code § 1102.5(b) which provides:
An employer, or any person acting on behalf of the employer, shall not retaliate against an employee for disclosing information, or because the employer believes that the employee disclosed or may disclose information, to a government or law enforcement agency, to a person with authority over the employee or another employee who has the authority to investigate, discover, or correct the violation or noncompliance, or for providing information to, or testifying before, any public body conducting an investigation, hearing, or inquiry, 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.
As I've previously observed, the statute is less than a model of clarity. In Hager v. County of Los Angeles, Cal. Ct. Appeal Case No. B238277 (Aug. 5, 2014) modified and certified for publication August 19, 2014, the Court of Appeal considered whether the statutory protection extends only to the first employee to make a covered disclosure. The question arose because the Court of Appeal in Mize-Kurzman v. Marin Community College Dist., 202 Cal. App. 4th 832 (2012) had construed the term "disclose" to mean to "reveal something that was hidden and not known". The Hager court, however, rejected the contention that Mize-Kurzman established a "first report" rule. This portion of the court's opinion is certified for publication.
In 2012, Congress amended the Whistleblower Protection Act (which protects federal government employees) to make it clear that a disclosure doesn't lose protection because "the disclosure revealed information that had been previously disclosed". 5 U.S.C. § 2302(f)(1)(B). Whistleblower Protection Enhancement Act of 2012, Pub. L. No. 112-199 (Nov. 27, 2012) § 101(b)(2)(C), 126 Stat. 1465, 1465-66.