President Obama's plan to expand health care coverage by raising taxes on the wealthy is drawing accusations that he wants to do it at the expense of charitable giving.

"I don't understand why the administration would try to create any disincentive that reduced any donations to charity," Sen. Pat Roberts, R-Kan., said.

Yet critics say that is exactly what the president's proposed budget will do by limiting the charitable giving tax break for families earning more than $250,000 per year.

The $634 billion down payment on expanding health care coverage would come from a $318 billion increase over 10 years in taxes on the wealthy, defined as couples making more than $250,000 per year and individuals making more than $200,000. 

The tax increase would occur in 2011 by reducing the benefit the wealthy get on tax deductions. For example, taxpayers in the current top tax bracket of 35 percent could see their tax deduction for every $1 given to charity drop from 35 cents to 28 cents.

The most recent IRS statistics from 2006 show that families earning more than $250,000, which represents less than 2 percent of all taxpayers, was responsible for about 28 percent of all giving, amounting to more than $81 billion dollars in charitable gifts.

Treasury Secretary Timothy Geithner sought to assure concerned senators Wednesday that taking away some of that group's tax break won't have a significant impact on their giving.

"Our view is that will have modest effect on actual giving and the most important thing you can do for overall charitable giving is make the economy strong," he said. "That has the biggest effect on giving as a whole."

Yet a study released this week by Bank of America and conducted by the Center on Philanthropy shows 47 percent of affluent households say they would give less if their tax deductions for charitable giving were eliminated. But 52 percent said their giving would stay the same if they didn't get the break.

That news comes at the same time 93 percent of professional fundraisers report that the economy is having a noticeable, negative impact on their efforts. Critics of Obama's plan say the timing couldn't be worse.

"It will reduce the contributions to charities as Americans are relying more on charitable assistance," Roberts said.

"We don't expect that people will stop giving altogether because of the proposed changes," Adriene Davis, communications manager for the Center on Philanthropy at Indiana University.

The Council on Foundations said in a statement, "We are opposed to proposals which will significantly depress incentives for charitable giving. In these hard economic times, we need to make sure tax and regulatory policy encourage growth in philanthropy."

The one silver lining may be a spike in short-term giving as donors try to beat the changes coming in 2011.

FOX News' Shannon Bream and The Associated Press contributed to this report.