The waiver over the years has helped the state - which has some of the most polluted cities in the country - to improve its air quality and become a model for battling climate change.
"Two courts have already upheld California's emissions standards, rejecting the argument the Trump Administration resurrects to justify its misguided Preemption Rule," California Attorney General Xavier Becerra said in a statement. "Yet, the Administration insists on attacking the authority of California and other states to tackle air pollution and protect public health." "Mr. President, we'll see you in court," he added.
Mary Nichols, chair of the California Air Resources Board, has warned that the rollback by the Trump administration will force millions of Americans to "breathe filthier air" if it prevails. "This is the fight of a lifetime for us," she said. "We have to win this, and I believe we will." Trump's announcement this week came after California reached a deal with major automakers to produce more fuel-efficient cars for the US market, infuriating federal authorities who claimed the agreement violated anti-trust laws.