In a direct challenge to California regulators and Bay Area environmentalists, the Trump administration Thursday ordered companies to ignore state requirements that businesses warn customers if their products contain glyphosate, a weed killer that has been linked to cancer.

The decision flies in the face of three California court rulings against Monsanto, which markets the chemical as Roundup. The agricultural giant faces more than 13,000 suits nationwide by users of Roundup, the world’s best-selling herbicide.

The U.S. Environmental Protection Agency announced it would no longer approve labels saying glyphosate is known to cause cancer.

“It is irresponsible to require labels on products that are inaccurate when EPA knows the product does not pose a cancer risk,” EPA Administrator Andrew Wheeler said in a statement. “We will not allow California’s flawed program to dictate federal policy.”

The state requires companies to warn customers about chemicals known to cause cancer under the Safe Drinking Water and Toxic Enforcement Act, approved by voters in 1986.

Glyphosate was classified as a probable human carcinogen in 2015 by the International Agency for Research on Cancer, which is part of the World Health Organization.

Lawyers for sick clients who were awarded tens of millions of dollars after suing Monsanto introduced evidence that glyphosate can cause genetic damage that leads to non-Hodgkin’s lymphoma. They claimed Monsanto ignored that information and published information “ghost written” by staffers denying the toxicity of the chemical.

Monsanto has steadfastly defended its product, pointing to a slew of studies that find no evidence of danger in glyphosate, and noting that the Environmental Protection Agency has never restricted Roundup.

“The Trump EPA’s disgusting campaign to hide glyphosate’s well-documented links to cancer from American consumers is hideous,” said Brett Hartl, the director of government affairs for the Center for Biological Diversity. “This is just the latest example of the Trump administration’s disturbing push to ignore peer-reviewed independent research by leading scientists in favor of whatever pesticide companies claim their own confidential research reveals.”

An Alameda County judge upheld a jury’s verdict in July that Roundup caused cancer in a Livermore couple, Alva and Alberta Pilliod, and awarded them $86.7 million.

Superior Court Judge Winifred Smith said there was clear evidence that Monsanto, after learning of the dangers, “made efforts to impede, discourage or distort scientific inquiry” by regulators. Monsanto’s parent company, the German pharmaceutical firm Bayer, said it would appeal.

A San Francisco Superior Court jury awarded $289 million last August to former school groundskeeper Dewayne “Lee” Johnson of Vallejo. A judge later reduced that award to $78.5 million. Then, in March, a federal court jury in San Francisco awarded more than $80 million to Edwin Hardeman of Sonoma County, whose cancer is in remission. That award was reduced to $25.2 million.

“The company has the responsibility for maintaining the accuracy of its label,” said Michael Baum, managing partner of the Los Angeles law firm Baum Hedlund, which represented Johnson.

Trump is “ignoring what the law says and neither he nor the EPA can override what Congress said is the company’s responsibility in the code of regulations for labeling,” he said. “We can hold Monstanto accountable for anything that’s false, misleading or negligent ... and failing to notify consumers that the active ingredients in Roundup is a carcinogen would be negligent.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com. Twitter: @pfimrite