The courts
class action
One lawsuit brought on behalf of everyone similarly injured. A judge must certify the class, and the judgment binds absent members who do not opt out.
In full
Class actions make small individual harms litigable: no one sues over a five dollar overcharge, but everyone together can. Certification requires numerosity, common questions, typical claims, and adequate representation, and the certification fight is usually the decisive moment, because a certified class changes the defendant's exposure by orders of magnitude.
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A plain-language explanation for civic education, not legal advice. When in doubt, the official source named above controls.