The Trump administration will propose scrapping Biden-era climate mandates requiring the nation’s power plants to curb planet-warming greenhouse gas emissions as soon as Wednesday, according to people familiar with the matter.

The Environmental Protection Agency is also set to advance a plan for easing limits on mercury and other toxic air pollution from the facilities, said the people, who asked not to be named because the measures aren’t yet public.

The proposals are among the administration’s most substantial deregulatory moves yet on environmental policy, coming as President Donald Trump prioritizes the expansion of domestic energy development, citing a massive surge in power demand from artificial intelligence.

Opponents of the Biden-era limits have argued the mandates unnecessarily force the closure of coal-power plants and discourage the construction of new gas-fired facilities. But environmentalists say Trump’s plans threaten to unleash pollution that imperils the climate as well as human health, effectively exposing people to more mercury, arsenic and other toxins that contribute to brain damage and cancer.

Former President Joe Biden had imposed the greenhouse gas curbs that effectively compel existing coal plants to capture nearly all of their carbon dioxide emissions — or close — by 2039. Trump vowed to “terminate” the requirements while campaigning last year.

Trump’s greenhouse gas proposal is set to assert that repealing the curbs would have no meaningful impact on public health and welfare because those emissions from coal- and gas-fired power plants are only a small share of planet-warming pollution and don’t contribute significantly to climate change.

The electric power sector is the second-biggest source of greenhouse gas emissions in the US, just behind transportation. Scientists say the world needs to rapidly curtail greenhouse gases to restrain global warming and avoid escalating, catastrophic consequences of climate change.

The EPA is also set to advance an alternative proposal that will assert that carbon capture and control technology embraced under the Biden rule is too expensive and not adequately demonstrated, according to people familiar with the matter. That’s in line with a view advanced by investor-owned utilities challenging the Biden measure.

“President Trump promised to kill the Clean Power Plan in his first term, and we continue to build on that progress now,” EPA Administrator Lee Zeldin said in a statement sent Monday. “In reconsidering the Biden-Harris rule that ran afoul of Supreme Court case law, we are seeking to ensure that the agency follows the rule of law while providing all Americans with access to reliable and affordable energy.”

The EPA declined to comment Tuesday, but later issued an advisory saying Zeldin plans to make a major policy announcement Wednesday at 2 p.m. New York time at the agency’s Washington headquarters.

The change poses more uncertainty for an electricity industry that is already facing unprecedented increases in demand and has also had to grapple with rapid policy shifts in Washington. The coming Trump proposal represents the federal government’s fourth attempt to address carbon dioxide emissions from existing coal plants, after the initial Obama-era Clean Power Plan was replaced in Trump’s first term with more modest limits, only to be reversed again by the Biden administration’s more aggressive push.

“As reported, these proposals would allow fossil fuel power plants to pour more pollution into our air — putting the health, safety and well-being of all Americans at risk,” said Vickie Patton, general counsel of the Environmental Defense Fund. “They would lead to more illnesses, which in turn would mean more days missing school and work, more visits to doctors and hospitalizations, and increased medical costs.”

The separate mercury measure would ease stringent standards that limit emissions of that metal as well as other hazardous air pollutants, necessitating pollution controls at coal-fired power plants. EPA limits on mercury pollution date to 2011, though requirements were strengthened under Biden last year.

Both proposals will be subject to a public comment period before they can be finalized and are likely to face legal challenges.