Technology companies Google, Apple, Microsoft and Amazon have declared support for the Obama administration in a lawsuit facing its central plan to combat climate change, saying the rule is needed to drive a transition to cleaner energy.
As large energy users, the companies filed a joint amicus brief to the federal Court of Appeals for the District of Columbia Circuit to support the Environmental Protection Agency as it defends its signature Clean Power Plan against a challenge by industry groups and more than half of US states.
"The Clean Power Plan reflects reasonable and attainable assumptions about the increasing availability of renewable generation in the nation's power sector," the companies wrote in the filing they submitted to the federal court on Friday.
The regulation is designed to lower carbon emissions from the US power sector by 2030 to 32 percent below 2005 levels, encouraging each state to replace dirtier fossil fuels with cleaner energy sources.
The rule is the United States' main tool to meet the emissions reduction target pledge it made at December's UN climate talks in Paris, but it was challenged by 27 states, along with business and industry groups in the DC Circuit court.
In February, the rule faced a major blow when the Supreme Court put it on hold pending the outcome of the litigation in the lower court. But the death of Justice Antonin Scalia a few days later renewed hopes for its survival.
A three-judge panel of DC Circuit court had unanimously rejected the same request for a stay that the Supreme Court accepted. The panel is viewed by lawyers on both sides as relatively favourable for the administration.
The technology companies, which all rely largely on renewable energy through power-purchase deals or their own facilities to power their energy-intensive data centres, said the EPA rule would help all businesses "invest and benefit from clean energy."
Earlier this week, the EPA filed a 200-page brief defending its rule, which said carbon emissions pose a "monumental threat" to the health and welfare of Americans.