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The opposition to one of President Trump’s most consequential regulatory rollbacks — a plan to weaken pollution standards for automobiles nationwide — widened on Tuesday when 24 governors, including three Republicans, urged the president to abandon his plan.

The governors’ plea adds to a chorus of criticism from an unlikely mix of voices, including not only environmentalists and labor unions but also some of the biggest automakers in the world. The two dozen governors include the leaders of four states — North Carolina, Pennsylvania, Wisconsin and Montana — that voted for Trump in 2016, helping propel him into the White House.

“Strong vehicle standards protect our communities from unnecessary air pollution and fuel costs,” the group wrote. The statement also noted that vehicles are “the largest source of carbon pollution in the United States,” a reference to the need to fight climate change by sharply reducing the amount of carbon dioxide pumped into the atmosphere.

The Trump administration’s rule changes, which are expected to land later this year, would weaken Obama-era rules that would have doubled the fuel economy requirement for new passenger vehicles by 2025 as part of Mr. Obama’s signature effort to fight global warming. President Trump has questioned the scientific consensus of climate change and has suggested that it is a hoax .