If you think the fight over health care legislation has been something to behold, just wait until debate over climate-change legislation gets under way in earnest.

Businesses are already dividing, and some of the biggest are taking some pretty large steps to stake out positions on legislation or regulations that would cap emissions of greenhouse gasses and set up a market to trade among corporations the rights to pollute.

“Energy, at this early stage—it’s an area where there’s just sharper cleavages among companies,” said Matthew J. Slaughter, associate dean of the Tuck School of Business at Dartmouth College. “And that’s different from many business issues.”

So far, it’s the utilities that are making the most noise. And they’re not on the side you may think they would be. These utilities favor legislation that has passed the House of Representatives and is sitting in the Senate awaiting the end of the health care debate. They’re voicing their concern by walking away from big business lobbies that don’t support climate-change action.

John Rowe, CEO of Exelon Corporation, one of the nation’s largest electric utilities, became the latest in a string of CEOs to say his company would quit the U.S. Chamber of Commerce—one of the biggest business lobbying groups with, over 3 million members—over positions the Chamber has taken toward climate change.

The Chamber has said it doesn’t oppose the principle of tackling global warming, but is concerned about the cost of such a change. And it has been particularly vocal in opposing an Environmental Protection Agency finding that, if Congress doesn’t act on climate change, the agency has the authority to regulate greenhouse-gas emissions. That finding arose from a Supreme Court ruling giving the EPA the order to treat greenhouse gasses as a pollutant under the Clean Air Act. The Supreme Court ruling was made during the Bush era, but the EPA didn’t make its finding until the beginning of the Obama administration.

What set off the latest wave of anger was a Chamber official’s call for a “Scopes Monkey Trial” about the science of climate change, a statement that Chamber officials have since repudiated.

Exelon’s CEO begged to differ with the Chamber’s position. “The carbon-based free lunch is over,” Rowe said. “Breakthroughs on climate change and improving our society’s energy efficiency are within reach.”

Rowe’s Chicago-based company is the nation’s largest provider of nuclear power, and a large portion of its electricity also comes from natural-gas plants. Natural gas is the cleanest burning of the fossil fuels, and nuclear power doesn’t emit any greenhouse gasses. So it’s not as much of a stretch as it may seem for Exelon to support a lower-carbon society. It could conceivably be a winner in such a society—able to trade emissions permits for a profit with heavier greenhouse-gas emitters.

But Exelon wasn’t the first of the big utilities to depart the Chamber.

PG&E Corp. CEO Peter Darbee last week launched a letter to Chamber CEO Thomas Donahue criticizing the Chamber’s recent positions on climate change and announcing that his company was leaving the organization. “Extreme rhetoric and obstructionist tactics seem increasingly to mark the Chamber’s public stance on this issue,” Darbee wrote. “PG&E considers climate change to be among the most serious issues ever for our company, our country, and the world. With this in mind, after careful consideration, we have come to the difficult conclusion that our differences over this issue have grown so significant that we will not renew PG&E’s Chamber membership next year.”