In a surprising decision, a federal judge last week blocked California from requiring Monsanto to put Proposition 65 warning labels on its Roundup products, ruling there is “insufficient evidence” that glyphosate—the active ingredient in the popular weed killer—causes cancer.

California’s Proposition 65 requires a “clear and reasonable warning” label on products that may expose people to a substance found on a published list of 900+ chemicals known to the State of California to cause cancer, birth defects or reproductive harm (the “Proposition 65 List”). California listed glyphosate on the Proposition 65 List in 2017, based primarily on a 2015 conclusion of the International Agency for Research on Cancer (“IARC”) that the chemical is a “probable” human carcinogen. Several other government health organizations, however, including the U.S. Environmental Protection Agency and the World Health Organization, have concluded there is no evidence that glyphosate causes cancer.

Monsanto and several agribusiness groups challenged California’s listing of glyphosate on the Proposition 65 List, as well as the attendant warning requirements that would become effective for glyphosate on July 7, 2018, claiming that the listing and warning requirements violate Monsanto’s First Amendment rights. Monsanto argued that by adding glyphosate to the Proposition 65 List and thereby requiring warnings, the state would compel Monsanto to make false, misleading, and highly controversial statements about their products.

U.S. District Judge William B. Shubb granted Monsanto’s request for preliminary injunction enjoining the state from requiring warning labels for glyphosate. Judge Shubb reasoned that California depended too much on IARC’s analysis that glyphosate is a “probable” carcinogen, stating that the required warning would “be misleading to the ordinary consumer” in light of contrary analysis by “virtually all other government agencies and health organizations.” Shubb continued, “the required warning for glyphosate does not appear to be factually accurate and uncontroversial because it conveys the message that glyphosate’s carcinogenicity is an undisputed fact, when almost all other regulators have concluded that there is insufficient evidence that it causes cancer.”

Curiously, Judge Shubb denied Monsanto’s request for an injunction barring California from listing the chemical on the Proposition 65 List. The First Amendment restricts government regulation of private speech, but does not regulate government speech. “California’s listing of chemicals it purportedly knows to cause cancer is neither a restriction of private speech nor government-compelled private speech,” Shubb said, adding it is the “upcoming July 2018 deadline for providing the Proposition 65 warning that compels private speech,” and that any harm to Monsanto would arise from the Proposition 65 warning requirements, not the listing.

While the court did not officially rule on the merits of the case, it appears Judge Shubb gave significant weight to the plaintiff’s arguments. When “California seeks to compel businesses to provide cancer warnings, the warnings must be factually accurate and not misleading. As applied to glyphosate, the required warnings are false and misleading,” likely violating Monsanto’s First Amendment rights.

It is unknown at this time whether the state will appeal Shubb’s decision.