The US Supreme Court has heard oral arguments in a landmark case that could determine whether federal pesticide regulation shields Bayer, the German chemical company behind Roundup (the world's most widely used weedkiller), from tens of thousands of lawsuits alleging it failed to warn users of cancer risks linked to its active ingredient, glyphosate. At the centre of the dispute is whether the Environmental Protection Agency's longstanding position that glyphosate is "not likely" a human carcinogen pre-empts state-level liability claims — a view contested by a 2015 World Health Organization panel that classified the substance as a probable carcinogen, with particular concern around non-Hodgkin's lymphoma among farmworkers and groundskeepers. The case has also exposed a political rift within the Trump administration, which has sided with Bayer in court despite pressure from the Make America Healthy Again movement, whose supporters rallied outside the court in what they called a "People vs. Poison" protest.