The world’s most widely-used weed killer can “probably” cause cancer, the World Health Organization said on Friday.

The organization’s cancer arm, the International Agency for Research on Cancer, said glyphosate, the active ingredient in the Monsanto herbicide Roundup, was “classified as probably carcinogenic to humans.” It also said there was “limited evidence” that glyphosate was carcinogenic in humans for non-Hodgkin lymphoma.

Monsanto, the world’s largest seed company, said scientific data did not support the conclusions and called on the group to hold a 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 for global regulatory affairs, said in a statement.