Esme Stallard is a news correspondent for the British Broadcasting Corporation.
Some of the EPA's power to reduce greenhouse gas emissions has been taken away.
President Joe Biden's climate plans were dealt a blow by the Supreme Court.
He said it would not undermine his efforts to tackle the climate crisis.
The case against the EPA was brought by West Virginia on behalf of 18 other mostly Republican-led states.
The agency didn't have the power to limit emissions in all states.
The power sectors in 19 states were worried that they would have to move away from coal.
The court ruled that the EPA did not have the power to impose such sweeping measures.
The Attorney General for Missouri said it was a big victory that pushes back on the Biden EPA's job-killing regulations.
Congress would have to say that it approves of the EPA's power to make these regulations in the future, according to the court. The EPA's proposed carbon limiting programmes have been rejected before.
In the past, the 19 states that brought the case have made little progress on reducing their emissions, which is necessary to limit climate change.
Since 2000, the states have only reduced their emissions by an average of 7%.
The Environmental Defense Fund said that the Supreme Court ruling undermined the EPA's authority to protect people from climate pollution.
The US is unlikely to achieve its climate targets without a change of policy from these states.
The president entered office on a pledge to increase US efforts on the environment.
He re- entered the country into the Paris Agreement on his first day in office.
He said that the country would reduce its greenhouse gas emissions by half by the year 2030.
While this decision risks damaging our nation's ability to keep our air clean and combat climate change, I will not relent in using my lawful authorities to protect public health.
This case will affect global efforts to tackle climate change. The US is the largest greenhouse gas emitting nation.
A spokesman for the UN said it was a setback in the fight against climate change.
The EPA's regulatory responsibilities in the US could be affected by this ruling.
Hajin Kim is an assistant professor of law at the University of Chicago.
Judges can say that Congress did not authorize the agency to do that.
The Supreme Court has held for a long time that judges should defer to government agencies when interpreting federal laws. The conservative majority has been chipping away at that practice recently.
The major questions doctrine states that a federal agency's discretion is limited when it comes to big issues that involve broad regulatory actions. The Clean Air Act would have allowed the EPA to issue sweeping regulations of the entire US economy if Congress had intended it.
The major questions doctrine was used by the majority of the court to strike down an attempt by the Biden administration to use a federal workplace law to mandate vaccinations.
The court will not approve of vague or broad laws being used to make regulatory changes. It has been difficult for Congress to pass new legislation recently. There may be an end to the time when presidents can find work-arounds.