(Reuters) - A U.S. congressional committee called on Thursday for the newly-elected director of the World Health Organization’s cancer research agency to testify at a July hearing on its operations in an ongoing dispute about the agency’s scientific conclusions.

In a letter to Elisabete Weiderpass, director of the International Agency for Research on Cancer (IARC), released in a press statement, the U.S. House of Representatives Science, Space, and Technology (SST) Committee, said the way the agency had operated under her predecessor “was an affront to scientific integrity”.

The letter asked Weiderpass to attend a committee hearing in July to help it “better understand” how she would manage the agency. The committee is chaired by Representative Lamar Smith of Texas.

IARC, which is based in France, wields great influence with its classifications of substances or lifestyles that may cause cancer. It says its mission is “to coordinate and conduct research on the causes of human cancer, the mechanisms of carcinogenesis, and to develop scientific strategies for cancer control”.

Weiderpass was named as IARC’s new director in May. She is due to take office in January 2019 when the current director, Christopher Wild, steps down after two five-year terms.

IARC was not available to confirm receipt of the U.S. congressional committee’s letter.

Thursday’s letter is the latest twist in an ongoing feud between IARC and two congressional committees. They began an investigation in 2016 after a number of IARC’s assessments - on substances such as coffee, mobile phones and processed meat cause cancer - sparked controversy.

The SST committee’s letter said these and other IARC evaluations had “bred distrust and confusion in the marketplace and amongst government regulators”.

The lawmakers said their increased concerns were fueled by the cancer agency’s review of glyphosate, the primary ingredient of the weedkiller Roundup, made by Monsanto’s.

A series of Reuters investigations last year showed how IARC, in reviewing glyphosate, excluded some data and findings that the chemical was not linked to cancer in people.

In December 2017, some members of congress warned that the U.S. government’s funding of IARC could be halted unless it was more open about its operations.

IARC previously responded to letters from the SST committee by declining to send representatives to give testimony but defending its methods as scientifically robust.

The agency says its “monographs” - the name it gives to its classifications of carcinogens - are “widely respected for their scientific rigor, standardized and transparent process and . . . freedom from conflicts of interest.”