The separate legal wrong of punishing a person for complaining about discrimination, reporting a violation, taking protected leave or helping in an investigation - a claim that often succeeds where the underlying complaint would not.
Nearly every civil-rights and workplace statute forbids not only the conduct it regulates but retaliation against a person for opposing that conduct or participating in a proceeding about it. An employee who complains of harassment, files a discrimination charge, testifies for a co-worker, requests an accommodation, takes family or medical leave, reports a safety violation or wage theft, or refuses to take part in something unlawful is protected from being punished for it. The protection covers the complaint whether or not the underlying conduct turns out to have been unlawful, so long as the person reasonably and in good faith believed it was - which is why a retaliation claim can succeed after the discrimination claim it grew from has failed.
The elements are protected activity, an adverse action, and a causal link between them. For retaliation the adverse action is defined broadly: anything that might dissuade a reasonable worker from making or supporting a complaint, which reaches a schedule change, an unfavourable transfer, exclusion from a meeting, a negative reference, or a report to immigration authorities, not only discharge or demotion. Causation is usually proved by timing, by a departure from the employer's normal practice, by shifting explanations, or by statements, and the employer answers by showing a legitimate reason that would have led to the same action regardless. Under the main federal employment statute the employee must show the protected activity was the but-for cause; some state laws use a lighter standard.
Retaliation protections extend beyond employment. Tenants are protected from eviction or rent increases for reporting code violations or exercising fair-housing rights; patients and nursing-home residents from reprisal for complaints; and the public from retaliation for exercising First Amendment rights against a government actor. Whistleblower statutes add their own, some with substantial rewards, and several require a complaint to a specific agency within a short window that runs from the retaliatory act.
Document the protected activity and the timeline before anything else: the date of the complaint, who received it, and every change in treatment afterwards. A lawyer will identify which statute's retaliation provision fits, because the deadlines and forums differ - some claims go to the EEOC, some to OSHA within a very short period, some straight to court - and will tell you whether to keep complaining internally, which builds the record, or to stop, which some employers use to argue the problem resolved itself.
Choose your state. Each link opens the directory page for the city in that state with the most currently published law firms in this practice area; a +n beside the city is how many other cities in the state also have one. The list is generated when this page loads, so a state whose listings have lapsed drops out rather than becoming a dead link.