The Environmental Protection Agency has completed a proposal to weaken a major Obama-era coal rule for regulating mercury and toxic air pollution from power plants, the agency confirmed Monday.

The White House’s Office of Management and Budget received the proposal from the EPA to relax the 2011 Mercury and Air Toxics Standards, or MATS, and it has initiated its review of recommended changes.

The EPA is proposing to rewrite the rule at the same time it is taking public comment on another more high-profile plan that would benefit the ailing coal industry. It is in the process of replacing former President Barack Obama's Clean Power Plan — his signature climate change initiative, targeting carbon pollution from coal plants — with a more modest measure designed to encourage plants to invest in efficiency upgrades that would allow them to burn less pollution, and exist longer.

While the mercury rule is less publicized, the coal industry considers it the most expensive air emissions regulation ever implemented, and is already spending $18 billion to comply with it, the EPA said.

States have been setting air pollution targets based on those investments and the rules remaining law. However, the coal industry blames it for forcing the closing dozens of coal plants across the country.

EPA is not looking to cancel the regulation entirely. Mercury is a neurotoxin that can especially harm the nervous systems of children and fetuses.

But the agency intends to provide legal justification for weakening it, and perhaps other air pollution rules, by proposing to change the way the it calculates the costs and benefits of regulations.

“The MATS rule was an egregious example of the Obama administration’s indifference toward required cost benefit analysis and dismissive attitude towards Supreme Court decisions that interfered with its political agenda to shut down coal,” EPA spokesman John Konkus told the Washington Examiner. “The draft proposed rule sent to [the Office of Management and Budget] is aimed at correcting the agency’s approach to weighing costs and benefits consistent with the court’s direction. It is not intended to roll-back or reduce important health protections associated with the continued reduction of mercury.”

In 2015, the Supreme Court blocked the Obama-era mercury rule, ruling the administration had failed to properly account for the costs of complying. The Obama administration reinstated the rule after conducting a new cost-benefit analysis requested by the court.

EPA wants to reverse an Obama administration finding that the agency must account for additional health benefits that result from regulations forcing the reduction of toxic pollution such as mercury from coal plants.

The Trump administration, and some conservatives and industry officials, say the EPA should not consider reductions in pollution outside the intended regulatory target as a benefit of a regulation. For example, power plants that have installed technology to reduce mercury have produced a “co-benefit” of cutting pollution from other hazardous pollutants, such as soot.

The Obama administration estimated it would cost roughly $9.6 billion a year to install the mercury control technology, and that reducing mercury could provide up to $6 million annually in health benefits. But it also projected billions of dollars' worth of additional health benefits annually from reductions in pollutants other than mercury.

The EPA proposal would not account for those side benefits when rationalizing a regulation.

Critics say EPA’s real aim is to handcuff itself, making it more difficult for the agency to consider the full spectrum of benefits from rules it makes.

“EPA is waging a war against accounting for the full range of benefits that flow from reducing pollution and the MATS proposal is just the latest of many fronts on which this war is being waged,” Joe Goffman, a former lead attorney at EPA in the Obama administration, told the Washington Examiner.

He suggested that EPA, in targeting the rationale behind the rule, could ultimately aim to weaken the emissions standards over mercury itself, allowing coal plants to operate in cheaper manner and emit more pollution.

“The emissions standards themselves are being targeted for rollback, and if they are, then power plants would likely have the option of running their pollution controls less frequently or at lower levels of efficiency, with the result being higher emissions than we are seeing now,” Goffman said.