"Car companies have lobbied Trump for months to roll back clean auto standards, putting profits ahead of the health of people and planet, and this is the result", Greenpeace USA spokesman Charlie Cray answered Wednesday.
The new EPA Administrator Scott Pruitt added that "these standards are costly for automakers and the American people".
Buttressing Brown's threats, California filed a motion late Tuesday to intervene in a new lawsuit brought by auto manufacturers against the EPA, a move immediately joined by New York State.
The attorneys general of California and NY announced Thursday that they are joining the legal defense of the emissions standards. "President Obama created such a labyrinth of rules and orders and regulations to cement his agenda across practically every agency", Tom Pyle, president of the American Energy Alliance, told Bloomberg.
For now, the announcement does not affect California's waiver under the Clean Air Act to impose a stricter standard for emissions, the administration official said, but the situation could change after the EPA makes a final decision.
"There is no more attractive sight than an American-made vehicle", said the President. Rolling back those demanding standards marks a big policy mistake on the president's part, however much it may please Detroit's automotive executives who have been pleading for relief from the higher miles-per-gallon requirements.
In 2012, automakers and federal regulators agreed to achieve an average 54.4 mpg across its entire fleet by the year 2025.
Trump's announcement comes amid a lobbying blitz from a coalition of the world's largest vehicle makers, which complained in a letter to the new administration that the existing EPA rules place unreasonable and expensive demands on the industry.
The regulations originated in California, with legislation passed in 2002, and were subsequently adopted by former President Barack Obama as national standards. Trump also wants to renegotiate NAFTA, which includes Canada and Mexico, but he did not mention those plans in Wednesday's remarks.
While Trump talked of ending the "assault" on the United States auto industry, it is unclear exactly what he is referring to.
President Donald Trump is interviewed by Reuters in the Oval Office at the White House in Washington, D.C., on February 23, 2017. But now automakers have a second chance to make their case.
Trump told the auto executives that while he's attuned to concerns about the environment, he doesn't want to stifle jobs.
"We want to be the auto capitol of the world again", emphasized Trump, "we will be, and it won't be long, believe me".
"We're going to pull back the EPA's determination because we don't think it's right and we're going to spend another year looking at the data in front of us", the official said.