The World Health Organization said that the world’s most widely-used weed killer can cause cancer.

The International Agency for Research on Cancer (IARC), the WHO’s cancer team, said that the active ingredient glyphosate in the Monsanto Co herbicide Roundup was classified as a carcinogenic to humans, according to Reuters.

Carcinogens are substances that can lead to cancer under certain levels of exposure.

They also said there was limited evidence that glyphosate was carcinogenic in humans for non-Hodgkin lymphoma.

Monsanto, the world’s largest seed company, said that the data did not support the conclusions and asked WHO for an urgent meeting to explain the findings.

“We don’t know how IARC could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe,” Philip Miller, Monsanto’s vice-president of global regulatory affairs, said in a statement.

Glyphosate is mainly used on crops such as corn and soybeans that are genetically modified to survive it and has been a hot topic recently. Last year, there was a passage on the country’s first mandatory labeling law for foods that are genetically modified in Vermont.

The U.S. government says that the herbicide is considered safe. In 2013 Monsanto requested and received approval from the U.S. Environmental Protection Agency for increased tolerance levels for glyphosate.

The weed killer has been detected in food, water and in the air after it has been sprayed. However, glyphosate use is generally low in and near homes where the general public would face the greatest risk of exposure.

Evidence for WHO’s conclusion was from studies of exposure, mostly agricultural, in the United States, Canada and Sweden that were published since 2001.

Monsanto’s stock price rose 0.3 percent on Friday to $115.75 after setting a four-month low on Thursday.