A recent U.S. Supreme Court ruling will likely pave the way for further legal challenges – and possible setbacks – to California’s groundbreaking clean air regulations and countless other federal environmental protections.

In a 6-3 decision last week, the Supreme Court struck down the so-called Chevron Doctrine, a long-standing precedent that directed U.S. courts to rely on federal agencies to interpret ambiguous laws. By invalidating the legal doctrine, the nation's highest court effectively stripped federal agencies like the Environmental Protection Agency of their power and gave U.S. courts more authority to independently decide whether newly enacted laws are consistent with federal law.

The six justices who voted to strike down the deference rule were appointed by Republican presidents, including Chief Justice John G. Roberts Jr., who wrote the majority opinion. The decision was dissented by Justice Elena Kagan, who dissented, as did Justices Ketanji Brown Jackson and Sonia Sotomayor—all of whom were appointed by Democratic presidents.

“What actions can be taken to address climate change or other environmental problems?” Kagan asked. “What will the country's health care system look like in the next few decades? Or the financial or transportation system? What rules will limit the development of AI?”

“From now on, the courts will play a crucial role in all areas of current or future federal regulation.”

After years of political disagreement and deadlock in Congress, the U.S. Environmental Protection Agency was forced to use decades-old environmental laws to craft modern regulations designed to slow climate change and combat pollution from new industries. Legal experts say the ruling could have a chilling effect on ambitious federal legislation, which will now be subject to a federal judiciary staffed by Trump-appointed judges.

It could also spell trouble for California's ambitious vehicle emissions regulations, which are based on Obama- and Biden-era interpretations of the Clean Air Act – a law last amended in 1990 that doesn't even mention greenhouse gases.

At least nine of California's air pollution regulations are still awaiting EPA approval, and the Supreme Court's decision adds to the tension in numerous legal battles over the state's zero-emission vehicle rules and other emissions standards.

“Although courts have a right to hear the agency's opinion, they do not have to respect it,” said Julia Stein, deputy director of the Emmett Institute on Climate Change and the Environment at the UCLA School of Law. “They can choose their own interpretation.”

The Supreme Court's ruling could also impact the Clean Water Act, which regulates water pollution.

The law refers to “navigable waters,” so there is uncertainty about whether habitats such as wetlands and streams are covered.

The ability of federal courts to change environmental protection laws shows how important it is for states to have their own laws, Stein said.

“We have our own legal system in California that is very strictly enforced by state agencies here at home,” Stein said of water regulation. “So even if something were to happen at the federal level, we have very robust protections at the state level to handle it.”