Though first proposed in 2012, the regulations encountered strong opposition from House Republicans, moderate Democrats and industry representatives—including the National Mining Association (NMA), whose directors will examine strategies with which to address the rule next week at their annual spring meeting.

White House climate change adviser Heather Zichal termed the latest EPA rules “historic” and aligned with the president’s objectives in his State of the Union address; Zichal didn’t address further rules for currently operating power plants, but suggested the EPA could consider them. “Energy and climate policy is going to be a top focus in (Obama’s) second term,” she told transportation industry officials in Washington recently.

The rules come amid new reports that energy-driven U.S. carbon dioxide (CO2) emissions fell to their lowest level in nearly two decades. Meanwhile, a recent report by the Energy Information Administration (EIA) found 5.3 billion tons of CO2 emitted by coal were lower than any year since 1994.

With the exception of 2010, the U.S. witnessed a steady decline in greenhouse gas emissions, according to EIA reports. The largest emissions drop took place in 2012, with competition from expanding natural gas, warmer winter weather and greater energy efficiency.