Sep. 29--As California Sen. Barbara Boxer prepares to unveil the Senate's climate change legislation on Capitol Hill today, the U.S. Chamber of Commerce -- a strong opponent of the global warming bill passed by the House and a likely foe of the Senate bill -- faces a high profile revolt by some of its members.

Earlier this month, San Francisco-based Pacific Gas and Electric took the extraordinary step of quitting the chamber because of its "extreme rhetoric and obstructionist tactics" as the debate over global warming legislation heats up in Congress.

Two other utility companies, New Mexico's PNM and Chicago's Exelon, followed PG&E's lead, and other companies are under pressure to join the exodus.

On Tuesday, the Green Century Equity Fund, which invests in athletic shoemaker Nike, urged Nike to "Just do it" and terminate its membership in the Chamber as well. Nike officials declined to comment.

"It makes sense to us for Nike to be the next company to pull out of the Chamber," said Emily Stone, a shareholder advocate for Green Century, noting that Nike has a strong brand as well as a reputation for supporting environmental sustainability. "What PG&E did was very important. The Chamber is a powerful organization, but there's safety in numbers."

The defections began when PG&E Chairman and CEO Peter Darbee sent a sharply worded two-page letter outlining why the privately owned utility, which provides gas and electricity

to 15 million customers from Eureka to Bakersfield, is pulling out of the chamber, which represents 3 million large and small businesses across the country and has one of the most powerful lobbying operations in Washington.

Darbee, who has invited leading climate scientists to meet with PG&E's board of directors in recent years, was particularly alarmed that the Chamber recently requested a public "trial" to weigh the scientific evidence that global warming endangers human health.

"We find it dismaying that the Chamber neglects the indisputable fact that a decisive majority of experts have said the data on global warming are compelling and point to a threat that cannot be ignored," wrote Darbee. "In our view, an intellectually honest argument over the best policy response to the challenges of climate change is one thing; disingenuous attempts to diminish or distort the reality of these challenges are quite another."

PNM, New Mexico's largest utility company, followed PG&E's lead a few days later. And on Monday, Exelon announced it was pulling out of the Chamber as well.