LONDON, (Reuters) - Two influential U.S. Congressmen have asked the World Health Organization’s cancer agency to get ready to testify about its work assessing if substances cause cancer, citing concerns about its “scientific integrity”.

External view of the International Agency for Research on Cancer (IARC) in Lyon, France, June 12, 2017. Picture taken June 12, 2017. REUTERS/Robert Pratta

Their letter to the International Agency for Research on Cancer (IARC), seen by Reuters and sent on Wednesday, is part of ongoing investigations by two Congressional committees into IARC that were fueled by the agency’s review of glyphosate, the primary ingredient of Monsanto Co’s weedkiller Roundup.

A letter to IARC director Chris Wild from the Republican chairmen of the House Committee on Science and the Subcommittee on Environment said they are “concerned about the scientific integrity” of IARC’s “monograph” program, which assesses whether various substances can cause cancer in people.

IARC, a semi-autonomous part of the WHO based in Lyon, France, has in recent years assessed whether substances as diverse as coffee, mobile phones and processed meat cause cancer - reports that have all caused controversy.

A spokeswoman for IARC said she could not immediately comment on whether the letter had been received.

IARC says its methods are scientifically sound and its monographs are “widely respected for their scientific rigor, standardized and transparent process and ... freedom from conflicts of interest”.

In a second letter seen by Reuters, the Congressmen, Lamar Smith and Andy Biggs, expressed concern that IARC’s assessment meetings, deliberations and drafts are not made public.

“It is an affront to scientific integrity to keep ‘confidential’ a scientific process that directly influences policy and individual taxpayers,” Smith and Biggs wrote.

“With United States’ taxpayer dollars funding (part of the monograph program), it is this (Science) Committee’s duty to ensure sound science and transparency within the agency.”

Citing data from the U.S. National Institutes of Health (NIH), the letter to Wild said that since 1985, IARC has received more than $48 million from NIH, more than $22 million of which went to the monographs program.

It added that Smith’s Committee on Science, Space and Technology may soon hold a hearing to receive testimony from IARC on how it conducts its reviews. It asked Wild to provide “names and contact information of IARC-affiliated individuals who would serve as potential witnesses for this hearing”.

The second letter, sent on Wednesday to acting U.S. Health Secretary Eric Hargan, asked his department to provide “all documents and communications between or among members of the IARC monograph program and any research institutes or agencies within HHS.”

In this letter, the lawmakers said their aim was to understand the extent to which the taxpayer-funded National Institute of Environmental Health Sciences and the National Institutes of Health are involved with IARC’s monograph process.

This is “to ensure scientific integrity and an honest use of taxpayer dollars”, the letter said.

In an assessment in 2015 that put it at odds with many government regulators, including those in the United States, Europe and Japan, IARC classified glyphosate as “probably carcinogenic”.

A Reuters investigation in October found that a draft of a key section of IARC’s assessment of glyphosate underwent significant changes before the report was made public.

Reuters also reported in June on how the chairman of the IARC glyphosate panel was aware of new data showing no link between the weed-killer and cancer in humans, but the agency did not take it into account because it had not been published.

The Congressional committee letters cited these Reuters investigations as well as other media reports, saying they revealed “troubling evidence” about the way IARC operates.

In the letters, Smith and Biggs asked IARC to respond by Nov. 8, and the department of Health and Human Services to respond by Nov. 15.