Costco is facing a lawsuit alleging unjust enrichment following revelations that the retailer charged customers for tariffs that were subsequently ruled unlawful. According to the legal complaint, while Costco collected these tariff-related fees from shoppers, the company now plans to retain the full refund amount it receives from the court decision rather than compensate affected customers. This practice raises questions about the retailer's obligation to return improperly collected funds to those who paid them. The lawsuit seeks to hold Costco accountable for what plaintiffs argue constitutes unfair business practices and consumer protection violations.