The decision of several major companies to quit the Chamber of Commerce over carbon emission regulation underscores the concern—and confusion—within Corporate America about how it will impact the bottom line.

Exelon, one of the country’s largest utilities, said Monday that it would quit the United States Chamber of Commerce because of that group’s stance on climate change. It was the latest in a string of companies to do so, perhaps a harbinger of how intense the fight over global warming legislation could become.

Amid a growing split in the business community over climate policy, Pacific Gas and Electric, a major California utility, is withdrawing from the United States Chamber of Commerce, citing “fundamental differences” with the chamber’s approach to global warming.