A U.S. appeals court on Monday handed 3M, Corteva Inc subsidiary E.I. du Pont de Nemours and Co and other manufacturers of toxic so-called “forever chemicals” a big win in their fight against legal liability for the substances, rejecting a lower court’s ruling that would have allowed about 11.8 million Ohio residents to sue the companies as a group.

The Cincinnati, Ohio-based 6th U.S. Circuit Court of Appeals vacated a lower court’s approval of the massive class action, which included virtually every resident of Ohio and put considerable legal pressure on the chemical manufacturers to settle the plaintiffs’ claims.

The court found lead plaintiff Kevin Hardwick filed too broad a complaint against the manufacturers, and had not shown per- and polyfluoroalkyl substances, or PFAS, found in his body could be traced directly to the defendants such as units of 3M, DuPont and others.

The court said Hardwick’s complaint “rarely” targeted the actions of any one company, and instead accused the companies collectively of contaminating the environment with the chemicals.

“Seldom is so ambitious a case filed on so slight a basis,” wrote Circuit Judge Raymond Kethledge, noting there are thousands of companies that have manufactured PFAS but just 10 listed as defendants in the case.

The appeals court instructed the lower court to dismiss Hardwick’s lawsuit, which had aimed to force the companies to pay for studies analyzing the health impacts of PFAS. The chemicals are used in a wide range of consumer products including non-stick pans and clothing and have been tied to cancer and other diseases.

The lawsuit also sought to establish a fund to monitor Ohio residents for health impacts from PFAS exposure.

A 3M spokesperson said the company is pleased with the decision.

Robert Bilott, an attorney for Hardwick, said the court’s decision runs “counter to what we know about the history of manufacturing of PFAS in the United States” and said they are evaluating whether to appeal.

Representatives for the other defendants did not immediately respond to requests for comment.

The chemicals are often referred to as forever chemicals because they do not easily break down in nature or in the human body.

The lawsuit is among thousands that have been filed against 3M, DuPont and others in recent years over alleged PFAS contamination.

3M agreed in June to pay $10.3 billion to settle hundreds of claims the company polluted public drinking water with the chemicals, while Chemours Co, DuPont de Nemours Inc and Corteva reached a similar deal with U.S. water providers for $1.19 billion.

The U.S. Environmental Protection Agency has called PFAS an “urgent public health and environmental issue,” and has taken steps to regulate PFAS, including in drinking water.