The exodus from the U.S. Chamber of Commerce continues. A third energy company is dropping its membership over the Chamber's short-sighted opposition to the clean energy bill.

Chicago-based Exelon announced today that it will not renew its membership with the U.S. Chamber of Commerce. That comes on the heels of last week's announcements from California's Pacific Gas and Electric Company (PG&E) and the Public Service Company of New Mexico (PNM) that they were were leaving the Chamber.

Of course, what it really follows is the Chamber's ridiculous demands for a "Scopes Monkey Trial" to debate whether climate change is real.

The New York Times has the full story, and the Wonk Room has good quotes from Exelon's CEO, John Rowe. You can also hear John Rowe on how climate change can be addressed affordably in an ad he did with us earlier this year.

All three refugees from the Chamber are members of USCAP (as is EDF). That means they're pushing for Congress to pass a cap on carbon pollution  — a move they see as a good business opportunity.

So, if three of its biggest members see a carbon cap as a money-making opportunity, why is the Chamber of Commerce opposing it?

See this story from NPR that explores whether it's because the president of the Chamber is also on the board of directors of Union Pacific — a company that makes a large part of its money shipping coal.