The Supreme Court on Thursday restricted a massive wave of lawsuits claiming the chemical giant Monsanto had a duty to warn consumers of alleged cancer risks from the world's most popular weed killer, Roundup. The justices ruled that federal law preempts cancer victims from bringing lawsuits against Monsanto in state courts, where most such claims are filed. The justices [also] ruled Monsanto was not required to offer a warning because the Environmental Protection Agency holds that Roundup's active ingredient, glyphosate, is not a cancer risk. "EPA has not required glyphosate-based pesticides like Roundup to include a cancer warning on their labels," Justice Brett M. Kavanaugh wrote for the majority. "Therefore, as a matter of federal law, Monsanto legally must use a label without a cancer warning unless and until EPA approves or requires a change." Monsanto has marketed Roundup as safe to spray in a t-shirt and shorts. The EPA has repeatedly found that glyphosate, which was first marketed in the 1970s, does not cause cancer. Glyphosate is used on about 300 million acres of farmland in the United States. In 2015 the International Agency for Research on Cancer, which is associated with the United Nations and World Health Organization, found glyphosate was "probably carcinogenic to humans." The agency found a likely link between non-Hodgkin lymphoma and glyphosate.