What the law counts as retaliation
Federal EEO law forbids punishing an applicant or employee for asserting the right to be free from discrimination. The EEOC’s 2016 enforcement guidance breaks a claim into three elements: protected activity, a materially adverse action, and a causal connection between them. Protected activity takes two forms. Participation means filing a charge, testifying, or taking part in an investigation or lawsuit, protected whether or not the underlying complaint had merit. Opposition means telling the employer, in a reasonable way, that you believe conduct is unlawful; it is protected if the belief was reasonable and in good faith, even if the conduct turns out to be legal.
The adverse-action element is broad. In Burlington Northern v. White (2006) the Supreme Court held that an action is materially adverse if it well might have dissuaded a reasonable worker from making or supporting a charge of discrimination, and that the protection is not limited to acts affecting the terms and conditions of employment. The EEOC lists reprimands, lowered evaluations, less desirable transfers, increased scrutiny, threats to report someone to immigration authorities, false rumors, and mistreatment of a relative as examples. Petty slights and minor annoyances do not qualify.
Causation is where most claims are won or lost. For private and state or local employers, retaliation must be a but-for cause of the action, though not the only cause; federal-sector Title VII and ADEA claims use a motivating-factor test. Proof is usually circumstantial: suspicious timing, explanations that shift, better treatment of coworkers who did not complain, and remarks that reveal animus. An employer stays free to discipline or fire for reasons unconnected to the complaint, which is why the record decides the claim.