It looked – at first – eerily like a routine news event. A man in a nondescript dark suit standing at a podium in one of the smaller meeting rooms on the 13th floor of the National Press Club. But then suddenly it wasn't.

"There is only one way to do business and that is to pass a climate bill quickly so this December President Obama can go to Copenhagen and negotiate with a strong position," said the speaker – who said he represented the US Chamber of Commerce.

The statement represented a complete repudiation of the Chamber's earlier opposition to climate change legislation. The hard line had triggered walk-outs from Apple and a handful of other high-profile companies in the past few weeks. The companies are trying to press the business organisation to support the bill by the senators John Kerry and Barbara Boxer that is to be debated by the Senate next week.

Or maybe not. Barely 20 minutes into the Q&A section of the press conference, an agitated spokesman for the Chamber burst into the room, screaming that the event was a hoax.

Score one for the Yes Men, who claimed responsibility for the prank. A number of news organisations and environmental groups were taken in.

Several green organisations tweeted or blogged on the about-face. Reuters news agency put out a straight news story about the Chamber's apparent U-turn, and the Washington Post and New York Times put the story on their news sites (both later removed the stories from their websites). CNBC actually sought – and got – comment from analysts. It also broke its programming to have a reporter read out the fake press release.

The spoof got under way with a press release inviting journalists to a morning news conference. Most reporters overlooked the misspelling of the Chamber president's name.

The phony spokesman said the Chamber was not happy with the bill before the Senate and would push for a carbon tax – not the greenest of positions. But he added: "If cap and trade is all we can get we have to take it so at least we can have something to put in President Obama's hands when he goes to Copenhagen."

He went out even further on a limb when he called clean coal "a hoax", saying the money would be better spent on solar energy research. "Clean technology has not only not been proven. It basically doesn't exist," he said.

It was about that time, the real Chamber spokesman burst into the room – and had a mild shoving match at the podium. "What happened today was a fraud and I believe illegal," Eric Wohlschlegel said. The spokesman said he learned of the hoax when a reporter came to the Chamber office looking for the press conference. Wohlschlegel said he immediately leaped into a taxi.

The spoof appears to be a joint production of the Yes Men, a group of activists who get their point across by impersonating greedy executives. Last month, the Yes Men took on global warming, producing fake copies of the New York Post with a banner headline declaring: "We're screwed". Two other activist groups also claimed credit.

In a statement today, the Yes Men said the stunt was intended to show how climate policy was being held hostage to corporate greed.

"The Chamber's position against climate legislation is completely troglodytic," said Andy Bichlbaum, who impersonated the Chamber spokesman. "The rest of the world sees the need for urgent action on the climate. The rest of the world's rich countries have pledged large emissions reductions. With scientists saying if we don't reduce carbon emissions, then sooner or later we're doomed, the Chamber represents corporate America at its most backwards."

The statement went on to flag up a Yes Men rally tomorrow morning and the release of their new documentary later this week.

And while a number of reporters still pressed Wohlschlegel for signs of a shift in the Chamber's position, he soon set them straight. The Chamber was as opposed to climate change legislation as ever.