Monsanto Company is fighting back against California’s recent decision to list glyphosate, the main ingredient in Monsanto’s popular herbicide RoundUp, as a cancer-causing chemical.

In late September, California’s Office of Environmental Health Hazard Assessment (OEHHA) issued a notice stating that glyphosate would be added to the state’s list of cancer-causing chemicals under the state’s Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65.

The decision was made after the International Agency for Research on Cancer (IARC), the research agency of the World Health Organization (WHO), published a report in March that classified glyphosate “as probably carcinogenic to humans.” State officials said this decision is a requirement following the IARC’s findings.

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[Read more: World Health Organization: Monsanto’s RoundUp ‘Probably’ Causes Cancer]

In response to the IARC report in March, Monsanto announced its plans to hire Intertek Scientific & Regulatory Consultancy to provide a third-party review of IARC’s claims. The Guardian later reported that a separate assessment performed by the German Federal Institute for Risk Assessments (BfR) “has drawn contrary conclusions from the IARC’s data. The BfR paper also relied heavily on unpublished papers provided by the Glyphosate Task Force, an industry body dedicated to the herbicide’s relicensing. Its website is run by Monsanto UK.”

[Read more: Monsanto Seeks Third-Party Review of Cancer Claims]

Monsanto filed formal comments on Tuesday stating that California’s plan may be illegal, and claimed that the state was insufficient in seeking valid scientific studies before moving forward with adding glyphosate to its Proposition 65 list. The IARC said that before making its classification, the agency had examined several scientific studies including two from Sweden, one from Canada and at least three from the United States.

Monsanto stated in its filing that California’s decision “has the potential to deny farmers and public agencies the use of this highly effective herbicide.” Monsanto further claimed that “global regulatory authorities… agree that glyphosate is not carcinogenic.”

The WHO’s classification of glyphosate as a probable cause of cancer has led to several lawsuits filed against Monsanto. A number of the lawsuits claim that the glyphosate in Monsanto’s Roundup herbicide caused cancer in individuals exposed to the ingredient. Monsanto responded that those claims are “without merit,” according to Reuters.