A group of seven consumers has filed a proposed class-action lawsuit against Costco Wholesale Corporation, accusing the retailer of selling Orgain Organic Protein Powder that is "tainted" with toxic heavy metals — including lead, cadmium and arsenic — without warning shoppers. Filed on Tuesday in federal court in Washington state, the suit alleges Costco breached consumer protection and false advertising laws by marketing the product as "high quality, clean, and nutritious" while failing to disclose the presence or risk of contamination. The case matters because it targets a major national retailer over a widely sold supplement and could set expectations for how such products are tested and labelled.

The plaintiffs argue that ordinary customers cannot detect heavy metals without expensive laboratory testing, and claim Costco "knew or should have known" about the contamination yet gave no disclosure. They cite findings from the Clean Label Project and Consumer Reports — the latter having reported that a vanilla bean Orgain powder exceeded its "level of concern" for lead — as well as independent testing commissioned by a plaintiff. Orgain said its products comply with applicable food safety standards and that trace environmental substances can occur in plant-based ingredients, adding it stands behind their safety and quality. Costco and Orgain did not immediately respond to the Guardian's requests for comment. The plaintiffs want the court to force Costco to disclose heavy metal levels and to stop selling such products without adequate warnings.