Analysts: Giving by Wealthy Would Decline Slightly Under Obama Budget Proposal

"Of course it's going to effect behavior," Zerbe said. "The charities recognize that. Everyone does.... People just don't have their feet on their ground if they're not recognizing that reality."

Still, Obama said his proposal should not deter giving.

"Now, if it's really a charitable contribution, I'm assuming that that shouldn't be a determining factor as to whether you're giving that $100 to the homeless shelter down the street," Obama said.