The Environmental Protection Agency said Wednesday that it will revisit a 2011 air pollution rule that has been blamed for closing dozens of coal-fired power plants around the country.

The Obama-era rule was part of what the utility industry once dubbed the “train wreck,” a group of EPA environmental rules that together required either massive upgrades to power plants, or for companies to shutter them.

The one that EPA is targeting is the Mercury and Air Toxics Standards, or MATS, which was meant to control air emissions and other pollutants like mercury from, primarily, coal and oil power plants.

The MATS rule is a prime component of what is commonly referred to by the coal industry and its supporters as the “war on coal.” President Trump and his Cabinet have frequently declared that the “war on coal is over.”

Colorado produced about 15 million tons of coal last year, up about 2 million from the year before, according to the Colorado Division of Reclamation, Mining and Safety.

The state’s leading power utility, Xcel Energy, has been scaling back its use of coal to produce electricity in favor of natural gas, the price of which has fallen in recent years.

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The D.C. Circuit Court of Appeals in April of last year granted the EPA’s request to delay litigation against the regulations, as the agency pondered whether it would make changes to the rule.

The draft MATS proposed rule is expected to be shipped over the the White House “soon” to undergo the interagency review process at the Office of Management and Budget, an EPA spokeswoman told the Washington Examiner.

After it’s vetted at the White House, EPA will release the proposed rule, which will provide the opportunity for public notice and comment.

The White House review process will take between 60 and 90 days, said spokeswoman Molly Block. The time frame could mean the proposal is rolled out in time for the midterm elections.

Block said there are some key elements that need to be addressed before taking action on MATS. First, EPA must assess the cost of the rule, as required by the 2015 Supreme Court decision Michigan v. EPA.

Second, the EPA must address how mercury and hazardous air pollutants are dealt with under the rule. “EPA knows these issues are of importance to the regulated community and the public at large and is committed to a thoughtful and transparent regulatory process in addressing them,” she said.

Sens. Tom Carper, D-Del., and Lamar Alexander, R-Tenn., sent a letter to EPA last week asking that the agency not propose rolling back the regulations.

“Keeping the current rule in place will provide much-needed certainty for the electric power industry and help protect the health of all Americans,” the senators wrote. “MATS has been a success, and changing the MATS rule just doesn’t make sense,” they added.

The letter followed one sent by the utility industry that asked EPA not to move forward with changes to the regulations. The industry wants EPA to evaluate technical changes to the rules, but “leave the underlying MATS rule in place and effective.”

The industry said it already spent $18 billion to comply with the regulations, and states have been making their air pollution targets based on those investments and the rules remaining law.

“By April 2016, virtually all coal- and oil-based generators completed their pollution control retrofits,” the letter added. “Certainty our members need as they continue to provide safe, reliable, affordable, and increasingly clean energy to their customers.”