California statutes prohibiting retaliation bar termination of (or other adverse employment action against) employees asserting their legally protected rights, exercising political affiliations, opposing unlawful discrimination at workplace, or seeking statutory redress (such as investigation of discrimination, harassment, etc.)
To show retaliation under California Fair Employment and Housing Act (FEHA), an employee must show that (1) he or she engaged in protected activity under FEHA; (2) he or she suffered an adverse employment action (such as demotion, transfer, suspension, termination or other action by the employer that materially affects the terms, conditions, or privileges of employment, and/or would tend to discourage a reasonable employee from complaining about the unlawful conduct at workplace); and (3) there is a causal connection between the protected activity and the adverse employment action.
FEHA specifically prohibits an employer from retaliating against employee for opposing any unlawful discriminatory practice prohibited by FEHA, and filing a complaint, testifying, or assisting in any proceeding under FEHA.
Note, that the great power of the anti-retaliation law is in that the employee only needs to show that he or she had a “reasonable belief” that the employer practice that the employee was opposing was unlawful. It doesn’t matter that a court later determines later that the practice complained of, or opposed to, is actually not illegal, as the California Supreme Court held in Yanowitz v. L’Oreal USA, Inc. (2005) 36 C4th 1028, 1043.