Exelon Corp., the biggest U.S. producer of nuclear power, said it will quit the U.S. Chamber of Commerce because the business group opposes federal climate change legislation, becoming the third utility to do so.

Exelon will not renew its membership in the Washington-based chamber, Chief Executive Officer John Rowe said today at a conference sponsored by the American Council for an Energy-Efficient Economy in Chicago, where the company is based. San Francisco-based PG&E Corp., the owner of California's largest utility, and PNM Resources Inc., which sells power in New Mexico, announced similar plans last week. PNM is based in Albuquerque.

Congress is working on legislation which would limit fossil-fuel emissions blamed for global warming by introducing a cap-and-trade system. The measure passed by the House in June would benefit companies with nuclear generators, such as Exelon and Entergy Corp., as they wouldn't bear the costs of the emissions that coal and gas plants would, according to New York- based Sanford C. Bernstein & Co.

"Putting a price on carbon is essential," Rowe said in a press release distributed by Business Wire today. "Inaction on climate is not an option."

The Washington-based chamber, which calls itself the world's largest business federation, asked the U.S. Environmental Protection Agency last month to release data on the science supporting climate-change regulations.

Eric Wohlschlegel, chamber's spokesman, wasn't available for an immediate comment.

Entergy plans to remain in the organization and convince other members to agree to emissions limits, Michael Burns, a spokesman for the New-Orleans based company, said in an e-mailed statement today.