An advocacy group seeking a ban on the world’s most widely used herbicide said Wednesday it is launching a U.S. public testing project to gather data on detectable levels of the herbicide in drinking water, human urine and breast milk.

The project, backed in part by organic organizations and critics of genetically modified crops, is the latest move in a brewing battle pitting agribusiness interests against consumer and environmental groups over the fate of the weed-killer called glyphosate.

Feed the World, the group behind the effort, is offering test kits that can be ordered for $119 each on its website, detoxproject.org/, and sent to a central laboratory for processing.

Director Henry Rowlands said the group is providing validated testing that meets regulatory standards. The results are to be used to pressure regulators and lawmakers to limit and eventually ban glyphosate, he said.

Glyphosate is the active ingredient in Roundup herbicide sold by Monsanto Co and is found in hundreds of products sold worldwide by many companies. It was first registered for use in the United States in 1974 and has long been considered safe by U.S. and many foreign regulatory bodies. It is widely used on crops, lawns, gardens and golf courses.

But some scientific studies have linked it to health problems, and last month a research unit of the World Health Organization classified glyphosate as “probably carcinogenic to humans.”

Monsanto spokeswoman Charla Lord said all labeled uses of glyphosate are safe and had no further comment about the Feed the World Project.

The U.S. Environmental Protection Agency (EPA) is concluding an extended review of glyphosate and has said it will issue a preliminary risk assessment for public comment later this year. The agency has the power to ban the herbicide, impose new limits on its use or keep current rules in place.

The U.S. government does not test for glyphosate residues in foods, though it does test for other pesticide residues. But a number of organizations have been sampling foods, urine and breast milk themselves, to try to determine the pervasiveness of glyphosate residues.

Glyphosate is used on corn, soybeans, sugar beets and other crops genetically altered to withstand it. It is also used by farmers growing wheat, oats and other crops. Its use has surged with the advancement of genetically engineered crops.