United States Supreme Court Potentially Weakens California Proposition 65

On June 25, 2026, the United States Supreme Court found that Missouri state claims regarding failure to warn about cancer was barred by the Federal Insecticide, Fungicide and Rodenticide Act (“FIFRA”). The plaintiff claimed that Bayer AG (parent company) and Monsanto Co. (manufacturer) failed to warn that Roundup could cause cancer. FIFRA does not require manufactures to about glyphosate, as the EPA has “repeatedly concluded that glyphosate is not likely to cause cancer.”

California’s Proposition 65 (“Prop. 65”) – the Safe Drinking Water and Toxic Enforcement Act of 1986 – requires warnings to consumers about exposure to chemicals linked to causing birth defects, reproductive harm, or cancer. As a result of the Supreme Court’s ruling, many have been discussing the implications for Prop. 65.

This ruling gives potential defendants an avenue to challenge Prop. 65 claims on federal preemption challenges. While California courts have been reluctant to intervene on preemption challenges in this area previously, this ruling may provide courts with sufficient grounds to uphold such challenges. The key to these challenges will be whether federal regulations, such as FIFRA, require warnings.

Stay tuned for future updates to such challenges being filed in response to Plaintiff Proposition 65 claims.