Democratic state attorneys general are backing the U.S. Environmental Protection Agency’s final rule to reduce pollution from coal-fired power plants, which is under legal attack by Republican state attorneys general who argue in court that the rule exceeds the agency’s statutory authority.

Twenty-one Democratic attorneys general, led by New York’s Letitia James and including the District of Columbia, filed a motion Thursday to intervene in a lawsuit 25 GOP attorneys general have brought in the U.S. Court of Appeals for the District of Columbia Circuit.