FIFRA Preempts State Rules

According to the opinion, the "Uniformity" clause of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) provides that a “state shall not impose or continue in effect any requirements for labeling or packaging in addition to or different from those required.” This FIFRA preemption clause was a key factor in the court’s decision.

“Because Durnell’s state tort claim would impose a pesticide labeling requirement ‘in addition to or different from’ the label required by EPA, FIFRA expressly preempts Durnell’s claim,” Justice Brett Kavanaugh wrote in the majority opinion.

The Glyphosate Debate: Cancer-Causing or Not?

The carcinogenicity of glyphosate is heavily debated. The World Health Organization’s (WHO’s) International Agency for Research on Cancer classified glyphosate as “probably carcinogenic to humans” in 2015. Since then, multiple juries have found Monsanto liable for failing to warn users about cancer risks (especially non-Hodgkin lymphoma) associated with Roundup exposure.

However, per the Supreme Court Monsanto v. Durnell opinion, “In 2017 and 2019, after [IARC] classified glyphosate as a probable carcinogen, EPA re-examined the issue but still adhered to its longstanding position on glyphosate… EPA’s assessment of glyphosate is shared by many other regulatory bodies around the world… All told, in accordance with EPA’s view that glyphosate is not likely to cause cancer in humans, EPA has not required glyphosate-based pesticides like Roundup to include a cancer warning on their labels. Therefore, as a matter of federal law, Monsanto legally must use a label without a cancer warning unless and until EPA approves or requires a change.”

Interestingly, in early 2026, the journal Regulatory Toxicology and Pharmacology retracted a paper from the year 2000 asserting the safety of glyphosate, which has been relied upon as a hallmark piece of evidence for regulatory approvals—including EPA’s—since its publication.

Also of note, in a February 2026 Executive Order, President Donald Trump urged the increased domestic production of glyphosate as a matter of “national defense.”

Decision Weakens States' Role in Communicating Pesticide Hazards

An amicus brief filed in the Monsanto v. Durnell case by a coalition of consumer, public health, and environmental protection organizations in April argued that eliminating state authority to require cancer warnings on pesticides would weaken longstanding federal–state roles in communicating pesticide hazards to consumers and agricultural workers. The brief cited analyses by the Center for Food Safety (CFS) and the Center for Biological Diversity (CBD) indicating that EPA has approved pesticides with identified cancer risks without requiring warning labels, raising concerns about gaps in federal oversight and transparency.

The amicus also referenced a 2022 federal court decision in a lawsuit filed by CFS that vacated EPA’s human health risk assessment for glyphosate, finding it inconsistent with the agency’s cancer evaluation standards. The filing groups asserted that this court decision revealed the weaknesses and limitations of federal oversight, further underscoring the importance of maintaining state-level authority to address potential risks.

“EPA's oversight of pesticides generally is the antithesis of the rosy picture [Bayer–Monsanto] paints: in reality, it is rife with loopholes, limitations, data gaps, delays, and lack of enforcement, making additional state enforcement vital,” said CFS.

Broader Implications of the Decision: Prop 65 Further Undermined?

Dennis Raglin, J.D., a Carlon Fields Shareholder who specializes in legal counsel regarding California's Proposition 65, explained to Food Safety Magazine the significance of the ruling and potential broader implications for state right-to-know chemical health warning laws.

“The ruling is significant as it federalizes product warning standards for all EPA-registered products—whether a state has current science it claims supports a warning, and even if it’s been over ten years since EPA reviewed the latest evidence of safety and cancer risk for glyphosate,” stated Mr. Raglin.

He continued, “The ruling strengthens the hand of those challenging Proposition 65’s constitutionality. Proposition 65 has already taken huge hits in the last few years, with federal courts finding Proposition 65 enforcement of four chemicals to be unconstitutional, including glyphosate. The others are acrylamide, titanium dioxide, and Cocamide DEA. Those federal courts have held that it is a violation of the First Amendment to require a company to carry a warning that contains information that is not factually correct and that is controversial, meaning, based on information that is not settled in the scientific community.”

Mr. Raglin provided an example of how Monsanto v. Durnell could affect future lawsuits challenging Proposition 65. According to Mr. Raglin, there are more than 950 Proposition 65-listed chemicals, many of which are regulated by EPA, including Bisphenol S. Hundreds of Proposition 65 notices of violation have been served alleging companies failed to warn customers about BPS in receipt paper, but BPS is regulated by two agencies: the U.S. Food and Drug Administration (FDA) as an indirect food additive and EPA under the Toxic Substances Control Act (TSCA). To date, EPA has not initiated any regulatory action to list BPS as a chemical of concern under TSCA, although Congress has granted EPA the authority to review and approve chemicals covered by TSCA, similar to FIFRA and pesticides.

"Does Monsanto mean claims against BPS are preempted?" Mr. Raglin questioned. "I like the odds in a court challenge to find out."