Labor unions criticized the Environmental Protection Agency’s new regulations on carbon emissions from power plants on Monday, highlighting growing tensions between the environmentalist and working class arms of the Democratic Party.

Those tensions have come to the forefront as leading Democrats embrace environmentalist policies backed by billionaire political donors that are generally opposed by members of the party’s rank and file base.

Some labor unions, groups generally considered loyally Democratic, rebelled on Monday after the EPA released its new regulations, which studies have suggested will carry hefty economic costs.

United Mine Workers of America (UMWA) president Cecil Roberts blasted the proposal, saying it would leave tens of thousands of the union’s members unemployed.

“The proposed rule … will lead to long-term and irreversible job losses for thousands of coal miners, electrical workers, utility workers, boilermakers, railroad workers and others without achieving any significant reduction of global greenhouse gas emissions,” Roberts said in a statement.

According to a UMWA analysis, Roberts said, the rule will cause 75,000 job losses in the coal sector by 2020, rising to 152,000 by 2035.

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