Like with most other civil rights, immigration status has no relevance to a person's ability to make a claim against his or her employer. Under California law, “all protections, rights, and remedies available under state law, except any reinstatement remedy prohibited by federal law, are available to all individuals regardless of immigration status who have applied for employment, or who are or who have been employed, in this state.” Cal. Lab. Code § 1171.5(a). The California courts has emphasized that California “statutes leave no room for doubt about this state’s public policy with regard to the irrelevance of immigration status in enforcement of state labor, employment, civil rights, and employee housing laws.” Hernandez v. Paicius (2003).
Therefore, any employer who thinks that he can get away with discriminating, harassing, retaliating or not paying correct to an employee whose visa has expired or wasn't approved risks being sued by that employee in exactly the same way as he would be by a US citizen or a permanent resident. It's important to remember the following distinction: it's true that it's illegal to hire or be hired for work without proper employment authorization. However, if an employee who is not authorized to work in the US was hired to work, then he has virtually the same rights as any other employee.