SACRAMENTO, Calif. (CN) – Effective July 7, California will list glyphosate, the active ingredient in the commonly used herbicide Roundup, as a probable carcinogen.

The California Office of Environmental Health Hazard Assessment (OEHHA) made the designation that glyphosate is a chemical known to cause cancer following an international agency’s designation.

Monsanto, the manufacturer of Roundup, says the listing of the chemical is “unwarranted on the basis of science and the law” and has vowed to fight the state agency.

The chemical manufacturer originally sued the state in Fresno County Superior Court, asking a judge to prevent the state agency from listing the chemical compound, but ultimately lost.

Although Monsanto has since appealed, the appeals court did not issue a stay that would prevent OEHHA from moving forward with the listing.

Monsanto has been reeling since the International Agency for Research on Cancer, a branch of the World Health Organization, listed glyphosate as a probable carcinogen in 2015.

The IARC’s finding prompted OEHHA to initiate the process toward listing the chemical compound under Proposition 65 — a law passed by California voters that requires the state to list chemicals that cause cancer.

The legal argument in Monsanto’s suit against the OEHHA hinged on whether the state agency could rely on the IARC as a source for listing, a particularly important distinction as the IARC is the only regulatory agency in the world to draw a connection between glyphosate and cancer.

The OEHHA has long maintained it relies on the IARC when developing its proposals of chemicals to list, and the court backed its decision.

However, recent reports cast suspicion on whether the IARC utilized all available science to reach its 2015 conclusions.

A recent report from Reuters indicated that the IARC scientist in charge of reviewing glyphosate’s potential to cause cancer knew of a recent study that demonstrated no link between exposure to the chemical and developing cancer, but disregarded it because it hadn’t been published yet.

The IARC’s listing has set off a series of lawsuits, including a class action suit in California in which several potential class members claim they developed a rare form of non-Hodgkin’s lymphoma from protracted exposure to Roundup.

OEHHA’s listing could require Roundup to be sold with a warning about its potential carcinogenic properties, although the agency has said it may only include warnings for industrial-scale applications of the herbicide, with household use remaining unaffected.

A spokesman for Monsanto said the company “will continue to aggressively challenge” the listing.

Monsanto’s appeal is pending in the California Fifth District Court of Appeal.

The OEHHA updates its list every year and currently includes approximately 800 chemicals.

The addition of glyphosate to the list garnered praise from environmental groups.

“California’s decision makes it the national leader in protecting people from cancer-causing pesticides,” said Nathan Donley, a senior scientist at the Center for Biological Diversity and a former cancer researcher. “The U.S. EPA now needs to step up and acknowledge that the world’s most transparent and science-based assessment has linked glyphosate to cancer.”