The Environmental Protection Agency proposed yet another weakening of an Obama-era regulation on Friday, this time targeting toxic chemicals from oil and coal-fired power plants.

The regulation in question, the Mercury and Air Toxics Standards (MATS), was established in 2011. It was the first set of federal rules to limit hazardous pollution from coal-burning and oil-burning plants, targeting chemicals like mercury, a neurotoxin that can lead to tremors, respiratory failure, and death. Coal power plants are the biggest emitters of mercury.

According to the EPA’s own projections, these rules save upward of 17,000 lives per year in the United States. The Center for American Progress found that MATS reduced mercury emissions from power plants by 81 percent since going into effect.

However, the energy industry and some states filed lawsuits to block MATS. One suit, Michigan v. EPA, fought its way to the Supreme Court. In 2015, the court ruled 5-4 in favor of Michigan, deciding that the EPA has to weigh the costs to industry of an environmental regulation against the benefits to society.

While the EPA’s latest proposal doesn’t repeal MATS outright, it starts to undermine its legal foundations. The EPA’s reasoning is that the current regulation as it stands is too costly and does not meet the “appropriate and necessary” standard.

The EPA said complying with MATS can cost power producers upward of $9.6 billion per year, but the benefits can only be quantified up to $6 million.

This is a vastly lower tally than what the Obama administration calculated when it issued the rule. They estimated $80 billion in benefits because they included the health side benefits of limiting toxic chemical pollution in addition to reducing the toxic chemicals themselves. This includes things like reducing emissions of particulate matter smaller than 2.5 microns in diameter (PM2.5), which can trigger breathing problems.

“EPA is not saying that it can’t consider PM2.5 co-benefits when it makes regulatory decisions,” said Jeff Holmstead, a former deputy administrator at the EPA under President George W. Bush, in an emailed statement. “They’re just saying that, in this case, where virtually all the benefits are ‘co-benefits’ of reducing a pollutant that is supposed to be regulated under other Clean Air Act programs, we can’t use these co-benefits to justify a regulation that is only supposed to be about hazardous air pollutants.”

By changing the cost-benefit analysis of MATS, the EPA is making it easier to challenge its implementation.

“If finalized, it will leave the mercury reduction requirements vulnerable to rollback or further legal attack, and it puts at risk years of progress to reduce exposure to a known neurotoxin that accumulates in the environment,” said Janet McCabe, who served as the acting assistant administrator for the Office of Air and Radiation at the EPA under Obama, in an emailed statement. “The proposal also sets a very troubling precedent for how the EPA evaluates the impact of policy on public health.”

Friday’s proposal is yet another example of the EPA’s strategy to play up the price tag of environmental regulations and to diminish their benefits. The EPA made similar revisions to its cost-benefit studies to justify undoing rules like the Clean Power Plan, which limits greenhouse gases from power plants, and to freeze fuel economy standards for cars and trucks.

When @EPA protests it is not killing the Mercury & Air Toxics Standards NOW, ask them why seek comment on doing so in a final rule & why ask industry ELEVEN TIMES whether EPA may or must “rescind” the safeguards against toxic air pollution from power plants that burn coal & oil. https://t.co/4ymfQPaCPk — John Walke (@jwalkenrdc) December 28, 2018

However, the fossil fuel power industry isn’t too enthusiastic about the prospect of undoing these rules. They’ve already spent $18 billion to comply with the Obama-era regulation. In a July letter to the EPA, industry groups asked the EPA “to leave the underlying MATS rule in place and effective.”

Nonetheless, air quality experts and environmental groups are worried. Many utilities have already baked in the costs of complying with these air-pollution restrictions into their electricity rates. Since it can be expensive to operate pollution control equipment, the concern for environmental activists is that a weaker toxic-chemical standard would allow power producers to shut off their scrubbers while still passing the costs on to customers.

The EPA will now take public comments on its proposal for 60 days after it is posted in the Federal Register. However, with the ongoing government shutdown, the Federal Register is not posting any new rules.