warningLong the subject of much controversy, California’s Proposition 65 law prohibits businesses from exposing Californians to chemicals “known to the State of California to cause cancer” without first providing a warning. California’s Office of Environmental Health Hazard Assessment (OEHHA) publishes a list of chemicals “known to the State of California to cause cancer.” By statute, that list must include substances designated as potential carcinogens by the International Agency for Research on Cancer (IARC), an international non-governmental entity.

Widely regarded as one of the safest herbicides ever developed, glyphosate is used worldwide in the cultivation of major crops. The federal government has approved the use of glyphosate for more than 250 types of agricultural crop applications, based on extensive scientific analyses of each specific use of the herbicide. The Environmental Protection Agency has repeatedly concluded that use of glyphosate in accordance with federal labeling instructions presents no unreasonable adverse effects on human health or the environment, and specifically that glyphosate is not a carcinogen.  Likewise, California itself has twice examined glyphosate in its own reviews—in 1997 and in 2007—and on both occasions concluded that glyphosate is “unlikely to pose a cancer hazard to humans.”

The same is true for every other regulatory body worldwide that has evaluated glyphosate, including regulatory agencies in Europe, Canada, New Zealand, Australia, and Japan, and the International Programme on Chemical Safety (the recognized authoritative body on these issues in the World Health Organization), as well as the Joint Food and Agricultural Organization and World Health Organization Meeting on Pesticide Residues. Earlier this month, a new study published in the Journal of the National Cancer Institute reinforced these findings.

Despite the worldwide consensus regarding the safety of glyphosate, in 2015 IARC concluded that glyphosate is a “potential carcinogen,” thereby automatically triggering California’s Prop 65 warning regime. IARC’s pronouncements have long been controversial among the scientific and public health communities. Among toxicology and regulatory experts who take great care not to exaggerate or inflame public understanding of cancer risks, there has been extensive public criticism of IARC’s recent glyphosate conclusions. Reuters has reported, for example, that the lead scientist chairing IARC’s glyphosate review knew of fresh data from the U.S. National Cancer Institute showing no cancer link to glyphosate but did not present that data to IARC’s specialists.

An appeal is currently pending in a California Court of Appeal of a lawsuit that argues Prop 65’s listing mechanism, because it allows a non-governmental entity to dictate an outcome, violates the California Constitution’s prohibition on such delegation (see WLF’s amicus brief in the case here and a WLF publication on it here).

Apart from the scientific controversy over IARC’s determination, the Prop 65 listing of glyphosate is also the subject of a new lawsuit filed this month in federal court. That lawsuit raises, among other legal claims, an as-applied First Amendment claim. As a general principle, the government can no more force private parties to speak than it can prevent them from speaking. Yet courts typically allow the government to compel warnings or disclaimers for commercial speech when the required statements are factually uncontroversial and neither misleading nor unduly burdensome.

For example, in R.J. Reynolds Tobacco Co. v. FDA, the U.S. Court of Appeals for the D.C. Circuit invalidated the Food and Drug Administration’s attempt to compel cigarette companies to include gruesome graphic warnings on cigarette packages—such as a man smoking through a tracheotomy hole—because those warnings were not purely factual, literally true statements but were instead intended to discourage consumers from purchasing cigarettes.

Likewise, in CTIA v. San Francisco, the Ninth Circuit struck down a San Francisco requirement that cell phone dealers inform consumers about issues pertaining to potentially dangerous radiofrequency energy emissions from cell phones, because the Federal Communications Commission had concluded that using cell phones is safe and San Francisco’s warning was essentially staking out a contrary position in an ongoing debate in the scientific community about the issue.

By contrast, in American Meat Institute v. USDA, the en banc D.C. Circuit upheld a USDA regulation requiring disclosure of the country of origin of certain meat products, concluding that such disclosures were purely factual and furthered the government’s goal of enabling consumers to choose American-made products.

In short, the government only prevails in compelling commercial speech when the compelled message is indeed “purely factual”—i.e., not subjective, and not a “fact” over which there is substantial controversy about its accuracy. Here, there should be little question that a California-mandated glyphosate warning is not purely factual, much less uncontroversial. Even if IARC believes that glyphosate is potentially carcinogenic, every regulatory body in the world disagrees, including agencies within the federal and California governments. Likewise, there is substantial public controversy regarding the methods IARC used to reach its outlier conclusion, including recent press accounts.

We are aware of no case where the government has been allowed to compel statements whose accuracy is as highly disputed as the glyphosate warning would be. A court is therefore likely to conclude that, as applied to glyphosate, the compelled cancer warning is unconstitutional under the First Amendment.

Also published by Forbes.com on WLF’s contributor page.