In a dramatic shift, the Chamber of Commerce announced Monday that it is throwing its support behind climate change legislation making its way through the U.S. Senate.

Only it didn’t.

An email press release announcing the change is a hoax, say Chamber officials.

Several media organizations fell for it.

A CNBC anchor interrupted herself mid-sentence Monday morning to announce that the network had “breaking news,” then cut away to reporter Hampton Pearson, who read from the fake press release.

Pearson quickly followed up with a second report saying the “so-called bulletin” was an “absolute hoax.” Smelling a rat, CNBC’s Larry Kudlow demanded to know whether the White House had been involved.

In a story posted Monday morning, Reuters declared: “The Chamber of Commerce said on Monday it will no longer opposes climate change legislation, but wants the bill to include a carbon tax.”

Reuters updated the story to acknowledge the hoax, but it was too late: The Washington Post and the New York Times had already posted the fake story on their Web sites.

"Reuters has an obligation to its clients to publish news and information that could move financial markets, and this story had the potential to do that,” said a Thomson Reuters spokesperson. “Once we had confirmed the release was a hoax, we immediately issued a correction, and in keeping with Reuters policy, the story was subsequently withdrawn and an advisory sent to readers."

The Yes Men, a left-leaning activist group that often impersonates officials from organizations they oppose, took responsibility for the hoax.

Andy Bichlbaum—an alias the activist uses for Yes Men demonstrations—told POLITICO that his group is targeting the Chamber for what he considers “retrograde” positions on climate change.

“Clearly, there is a question of who is hoaxing who,” Bichlbaum said. “I think the Chamber is hoaxing the American public at this point.”

Bichlbaum said that activists will continue targeting the organization. Bichlbaum said the Yes Men got help with their prank from members of the AVAAZ Action Factory, an activist group, and BeyondTalk.net, an environmental website.

AVAAZ has not returned calls for comment. But a post on the group’s Web site said it had plans to “make this the worst Monday ever for the anti-climate PR machine at the U.S. Chamber of Commerce. “

The fake Chamber press release distributed to reporters Monday looked like an authentic document from the Chamber, with a logo and contact information for follow-up stories. But there were clues that it was false. The name of Chamber president Tom Donohue was misspelled, and the individuals listed as press contacts do not work at the Chamber.

The press release falsely quoted Donohue as saying : “We at the Chamber have tried to keep climate science from interfering with business. But without a stable climate, there will be no business. We need business more than we need relentlessly higher returns.”

And the press release said that the Chamber is implementing an “immediate moratorium on lobbying and publicity work opposing climate legislation” – and suggested that high-profile defections from Apple, Nike PG&E and other companies played a role in the decision.

In fact, the Chamber opposes – and continues to oppose – the cap-and-trade bill passed by the House in July.

The fake press release said that Donohue would be announcing the policy shift in a speech at the National Press Club Monday morning. Donohue gave no such speech, but Bichlbaum and other imposters posing as Chambers officials did attempt to hold a press conference at the facility Monday.

It came to an abrupt end when a real representative of the Chamber showed up to confront the imposters.

Bill McCarren, general manager of the National Press Club, said that an organization calling itself the U.S. Council on Climate – same initials as the Chamber– booked space at the club on Friday. On Monday, the group asked that its contact information be changed: The new information included a number for the real Chamber of Commerce, tipping off the press club that there was a hoax taking place.

The group used the Chamber’s logo in staging the new s conference, and also had a sign-in sheet for reporters that listed it as a Chamber of Commerce event.

McCarren said the group paid for the room—the typical cost is about $500—and would not be permitted to hold future events.

“We, as an organization, meant no offense to the Chamber of Commerce,” McCarren said, adding: “We did not mean to participate, willingly or unwillingly, in a spoof a news conference.”