CHARLESTON, W.Va. (AP) — The head of the national mine workers’ union on Friday condemned what he characterized as an effort by House Republicans to block enforcement of a long-awaited federal rule directed at curbing workers’ exposure to poisonous, deadly rock dust, calling it “a direct attack on the health and safety of coal miners.”

United Mine Workers of America International President Cecil E. Roberts said a budget provision — approved by a U.S. House subcommittee Thursday — prohibiting the Department of Labor from using funding to enforce a silica dust rule operators must be in compliance with next year is “morally reprehensible” and that the action “undermines the principles of fairness and justice that our country stands for.”

“It is difficult for me to understand how certain members of Congress could possibly be supportive of more miners dying a suffocating death as a result of being forced to breathe this dust,” Roberts said in a statement.

Silicosis, commonly referred to as black lung, is an occupational pneumoconiosis caused by the inhalation of crystalline silica dust present in minerals like sandstone. Finalized in April by Acting Labor Secretary Julie Su, the U.S. Mine Safety and Health Administration, or MSHA, rule cuts by half the permissible exposure limit for crystalline silica for an eight-hour shift.

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The regulation is in line with exposure levels imposed by the Occupational Safety and Health Administration on construction and other non-mining industries. And it’s the standard the Centers for Disease Control and Prevention was recommending as far back as 1974. The U.S. Department of Labor began studying silica and its impact on workers’ health in the 1930s, but the focus on stopping exposure in the workplace largely bypassed coal miners.

Su said in April that it is “unconscionable” that America’s miners have been forced to work without the protections for so long: “We’re making it clear that no job should be a death sentence.”

The black lung problem has only grown in recent years as miners dig through more layers of rock to get to less accessible coal, generating deadly silica dust in the process. Silica dust is 20 times more toxic than coal dust and causes severe forms of black lung disease even after a few years of exposure.

The increased drilling has meant that severe forms of the disease are being identified even among younger Appalachian miners, some in their 30s and 40s. An estimated one in five tenured miners in Central Appalachia has black lung disease; one in 20 has the most disabling form of black lung.

On Thursday, the House subcommittee did not debate the bill containing the silica dust rule enforcement block before advancing it. A spokesperson for Labor, Health and Human Services and Education Subcommittee Chair U.S. Rep. Robert Aderholt, a Republican representing Alabama, did not return an email request for comment Friday. National Mining Association spokesperson Conor Bernstein said in an email Friday that officials at the organization, which represents operators, haven’t been “involved in this legislation and, therefore, are not in a position to comment.”

Mine safety advocates are scrambling to meet with lawmakers before the bill is scheduled to go before the full House Appropriations Committee on July 10. It would have to be greenlit by that committee before going to the full chamber.

Quenton King, federal legislative specialist for Appalachian Voices, a nonprofit that advocated for the silica dust rule, said the protection is essential to protecting not only coal miners in central Appalachia but metal and nonmetal miners across the country. He said that if allowed to be enforced, it will help save thousands of lives.

“To willfully prevent MSHA from doing that would literally be killing miners,” he said.

West Virginia Attorney Sam Petsonk, who has represented coal miners who were diagnosed with black lung after companies violated safety violations, said he sees workers every day who have fewer than 10 years of mining experience diagnosed with end stage, fatal silicosis.

“This is a policy decision by the entire Republican party leadership to throw America’s miners to the dogs,” he said. “It’s insulting and really unfair to our communities for them to do this to us. And it’s certainly inconsistent with the idea that the Republicans are trying to help coal miners and coal mining communities.”