Wealthy Wall Street financiers and other business figures provided crucial support for Mr Obama during the election, backing him over the Republican candidate John McCain as the right leader to rescue the collapsing US economy.
But it is now dawning on many among them that Mr Obama was serious about his campaign trail promises to bring root and branch reform to corporate America - and that they were more than just election rhetoric.
A top Obama fundraiser and hedge fund manager said: "I'm appalled at the anti-Wall Street rhetoric. It was OK on the campaign but now it's the real world. I'm surprised that Obama is turning out to be so left-wing. He's a real class warrior."
Chris Edwards of the Cato Institute, a free enterprise think tank, said Democrats in Congress were unnerved by the president's latest plan to raise $210 billion over 10 years from multinational corporations.
The money is needed to pay for a national debt that will double over the next five years; and triple over the next 10 years to $17.3 trillion. But the crackdown already faces fierce Democratic resistance.
"These big companies are based in New York Boston, Seattle and Silicon Valley, where Democrats dominate," Mr Edwards said. "Obama's tax plan is already cleaving him from his big corporate supporters," he said.