Chemical giant Monsanto has argued for years that if the U.S. Environmental Protection Agency approves a pesticide label without requiring a cancer warning, states cannot hold its manufacturer liable in court for failing to warn consumers about cancer risks. The U.S. Supreme Court agreed, in a ruling issued on June 25, 2026, though some members of Congress are taking steps to override that ruling.

Between 2009 and 2019, the EPA repeatedly concluded there is no evidence that glyphosate causes cancer in humans. The agency has, therefore, allowed glyphosate-based weed killers, including Monsanto’s Roundup, to remain on the market without a cancer warning on its label. That’s despite a 2015 report from the International Agency for Research on Cancer, a branch of the World Health Organization, that classified glyphosate as “probably carcinogenic to humans” based on “limited” evidence of cancer in humans from real-world exposure and “sufficient” evidence of cancer in experimental animals. A 2025 study had similar findings in lab rats.

Several U.S. lawsuits have used the 2015 report to win legal cases claiming that Monsanto failed to warn them of the chemical’s dangers. One of the first, Hardeman v. Monsanto Co., ended in a US$80 million verdict against Monsanto in 2019. The jury found that Edwin Hardeman, a California man who used the weed killer on his properties, had proved that Roundup had caused his cancer and that Monsanto had failed to warn consumers of the dangers of its product. That finding was upheld on appeal.

In the years since, Monsanto, now owned by German chemical giant Bayer, has paid out over $10 billion to settle about 100,000 claims from people who said their health was harmed after they were exposed to Roundup. But Monsanto continues to say – and the Supreme Court agreed – that a federal law passed in 1947 and significantly amended in 1972, the Federal Insecticide, Fungicide, and Rodenticide Act, bars states from imposing any labeling requirement beyond what the federal government........

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