As the Senate gets set to take up climate change legislation, one of the key opponents of serious efforts to stop global warming may find its clout on the issue badly weakened.

That's because in recent weeks, several high-profile members of the Chamber of Commerce have gone public over their disagreement with the group's position, with some leaving the Chamber altogether over the issue.

This week, Exelon Corp., the country's largest utility company, announced it was quitting the group because of its opposition to action on global warming. In doing so, it joined two other utilities, PNM Resources Inc. and Pacific Gas & Electric Co, whose CEO last week called the Chamber's position "extreme."

Then on Wednesday, Nike, also citing the global warming issue, said it would resign its position on the chamber's board of directors, but would remain a member of the group. And a GE spokesman told Politico that "the Chamber does not speak for us on climate legislation," but that GE, too, would remain a member.

The Chamber's woes began when an official with the group recently called for a "Scopes Monkey Trial of the 21st century" to investigate whether man-made warming is occurring -- a fact which is no longer in doubt. In response, environmentalists began pressuring the Chamber's members to quit the group, or at least distance themselves from its position on the issue -- and they appear to be having some success.

In a letter to the Chamber, PG&E wrote:

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. In our opinion, 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.

In what looks like a damage control effort, the Chamber's CEO this week reiterated the group's position on the issue, asserting that the Chamber doesn't oppose all efforts to deal with climate change -- only those, like the Waxman-Markey bill, and its likely equivalent in the Senate, that are actually being considered.

Of course, there may be different commercial imperatives in play in each case. Exelon, for instance, is one of the country's largest producers of nuclear power, so it has an incentive to get on board early with efforts to encourage alternative energy. Nike, for its part, has an educated customer base that may punish it for appearing to support a discredited and irresponsible stance on a crucial issue of our time.

But ultimately, what matters is whether the Chamber's ability to fight action on global warming is impeded when the Senate takes up the issue. And it's not a stretch to think it could be.