Final answer:
Interest groups use litigation as a strategy of influence by filing amicus curiae briefs, financing class action lawsuits, and bringing suits on behalf of the group.
Step-by-step explanation:
Interest groups use litigation as a strategy of influence in several ways. First, they file amicus curiae briefs, or "friend of the court" briefs, to present legal arguments supporting a particular position or outcome. These briefs are used when the interest group is not directly involved in the case but will be affected by the decision.
Second, interest groups finance class action lawsuits, which allow plaintiffs with similar circumstances to combine their cases. This strategy helps share costs and cover individuals who may not be aware they have a case. Lastly, interest groups may bring a suit on behalf of the group itself, advocating for their interests in court.