California can require Monsanto to label its popular weed killer Roundup as a possible cancer threat even though the chemical giant insists it poses no risk to people, a judge tentatively ruled Friday. California would be the first state to order such labeling if it carries out the proposal. Monsanto had sued the nation's leading agricultural state, saying California officials illegally based their decision for carrying the warnings on findings by an international health organization based in France. Critics take issue with Roundup's main ingredient, glyphosate. It is sold in more than 160 countries, and farmers in California use it on 250 types of crops. The chemical is not restricted by the U.S. Environmental Protection Agency. But the International Agency for Research on Cancer, a Lyon, France-based branch of the U.N. World Health Organization, classified the chemical as a probable human carcinogen." Shortly afterward, the most populated U.S. state took its first step in 2015 to require the warning labels. Once a chemical is added to a list of probable carcinogens, the manufacturer has a year before it must attach the label. Dozens nationwide ... are suing Monsanto, claiming the chemical gave them or a loved one cancer.