By Ben Geman - 06/13/13 06:54 PM EDT
The letter urges Obama to impose emissions standards on the nation’s existing power plants, which is a top priority for climate change activists.
The Environmental Protection Agency, in a 2010 legal settlement, said it intends to address existing plants. But the Obama administration has declined to provide a time frame for action, frustrating environmentalists and liberal Democrats.
The senators also press Obama to issue delayed rules that set emissions standards for new power plants, a measure that will add to the already large hurdles facing any proposal to build new coal-fired plants.