The case could help determine the future of thousands of lawsuits against the maker of a popular herbicide over claims that it causes cancer.
The Supreme Court appeared divided on Monday during arguments in a dispute that could determine the fate of thousands of lawsuits that claim a widely used weedkiller causes cancer.
The case is the latest turn in a yearslong legal battle over safety concerns with the weedkiller Roundup. Developed by Monsanto in the 1970s, the herbicide is the focus of the lawsuits, which allege that it causes non-Hodgkin lymphoma.
The dispute before the justices stems from a 2019 lawsuit brought by a Missouri gardener, John Durnell, who used Roundup for years. Mr. Durnell claimed in his suit, filed in state court, that glyphosate, a chemical in the weedkiller, caused him to develop cancer.
During Monday’s oral argument, several of the justices expressed skepticism of arguments by Bayer, the German conglomerate that acquired Monsanto in 2018, and the Trump administration, which joined the case in support of the company, that federal rules requiring herbicide safety labeling should bar people from filing state-level claims that accuse companies of failing to warn consumers of dangers.
Chief Justice John G. Roberts Jr. asked a lawyer for the Trump administration whether states would be blocked from taking action if new scientific information raised alarms about a product.
“The states cannot do anything?” the chief justice asked.
Sarah M. Harris, a principal deputy solicitor general, responded that it would be problematic to have each state “jumping the gun” to come to its own conclusion about whether a product caused cancer.