Facing the Obama administration's so-called "war on coal," some utility officials are warning that fewer coal-fired power plants could leave the U.S. power system vulnerable to blackouts in the near future.

The officials warn that intense summer heat or extreme winter cold could soon be too much for the system to handle.

"I worry about the potential of brownouts and blackouts if we're ... actually depending on this generation that's going to be retired," Nick Akins, from American Electric Power, told Fox News in an interview.

Pro-coal advocates say the administration's focus on its environmental agenda challenges the reliability of the nation's power grid.

"Regulation from five years ago is closing about 20 percent of the coal plants. Regulations being proposed now could close an additional 20 percent of coal plants. And that creates huge stresses -- we're just not ready for anything like that in this country," Mike Duncan, from the American Coalition for Clean Coal Electricity, told Fox News.

However, the EPA says government studies indicate there will be more than enough electricity-generating capacity to meet the nation's needs.

Asked about future regulations, EPA Administrator Gina McCarthy suggested the agency is trying to be careful.

"Nothing we do can threaten reliability. We have to recognize that in a changing climate like the one we have recently been experiencing, it is an increasing challenge to maintain a reliable energy supply," McCarthy said.

Still, considering this past winter's severe cold and "Polar Vortex," Alaska Republican Sen. Lisa Murkowski noted at a Senate hearing this week that the system was at its limits.

"Eight-nine percent of the coal electricity capacity that is due to go offline was utilized as that backup to meet the demand this winter," Murkowski said.

And coal country Democratic Sen. Joe Manchin, of West Virginia, clearly has his concerns.

"Add the fact that EPA is proposing new source performance standard, what this is going to do will effectively ban the construction of any new coal plants," Manchin said. "How do we keep the lights on so people's lives will not be in danger?"

Even Minnesota Democratic Sen. Al Franken, a former comedian, argues this is no laughing matter.

"We need state flexibility in addressing those kind of issues, especially on the new rules that the EPA will make on existing coal fire plants," he said. "We're talking about grid security -- it's a serious issue."