When people say that environmentalists twist or delete facts in order to achieve their ends, this is what they’re talking about: one scientist withheld crucial information so that the World Health Organization would condemn the agriculture business giant Monsanto for causing cancer. Here's the story:

Monsanto sells a weedkiller called glyphosate, which is popularly known as RoundUp. Roundup is the world’s most widely used pesticide; roughly 250 million pounds is sprayed on U.S. crops every year.

Although the U.S. Environmental Protection Agency and the European Food Safety Authority had declared that Roundup does not cause cancer, suddenly, in 2015, the International Agency for Research on Cancer (IARC), part of the U.N.’s World Health Organization, declared RoundUp a probable carcinogen. That prompted 184 plaintiffs in California to sue Monsanto, triggering hundreds of other entities to sue Monsanto and use the IARC claim to buttress their case.

But wait: according to Reuters, the scientist who headed the IARC’s review panel on glyphosate knew of an important study, on which he himself served as a senior researcher, that strongly suggested Roundup did not cause cancer, but he withheld the information from the RoundUp review panel.

When Aaron Blair, an epidemiologist from the U.S. National Cancer Institute, served as the chairman at a meeting of 17 specialists at the International Agency for Research on Cancer in France in March 2015, he refused to inform the IARC about the study, allowing them to think glyphosate caused cancer.

As Mother Jones reports, “In a sworn deposition given in March this year in connection with the case, Blair also said the data would have altered IARC’s analysis. He said it would have made it less likely that glyphosate would meet the agency’s criteria for being classed as ‘probably carcinogenic.’”

IARC made excuses for Blair, saying the agency’s policy prevented it from using unpublished data when making its decisions. Blair tried to get off the hook by claiming that the data wasn’t published before the IARC made its decision because there was too much data to fit in one paper.

Michael Eisen, the founder of the Public Library of Science, told Mother Jones that the IARC rule was “silly,” adding, “This is a board of people whose job it is to assess evidence, so they should be able to do that before it’s published. The broader issue is that they seem eager to have reached the conclusion that they reached.” Eisen said that the idea that the data had to be peer-reviewed before the panel could weigh it was specious, as the review panel itself was comprised of experts.

Reuters added:

David Spiegelhalter, a professor of the Public Understanding of Risk at Britain's University of Cambridge, said there was “no apparent scientific reason” for not publishing the data. Bob Tarone, a retired statistician who worked alongside Blair and others at the National Cancer Institute for 28 years before moving to the for-profit International Epidemiology Institute, said he could find “no ready explanation in terms of the available scientific evidence” for the data not to have been published.

Yet despite the fact that IARC’s decision was based on incomplete evidence, the agency will not retract its claim that RoundUp causes cancer. Reuters reports, “IARC told Reuters that, despite the existence of fresh data about glyphosate, it was sticking with its findings."

Look out: on Thursday, at an EPA budget hearing, Rep. Tom Cole (R-OK.) asked EPA Administrator Scott Pruitt to look into the problem.

Eisen concluded that the IARC will be viewed as less trustworthy now, asserting, “This is going to end up undermining people’s confidence in this agency’s ability to do this well, They don’t seem interested in getting to the bottom of these things. These decisions seem based in politics.”