Billionaire investors Warren Buffett and George Soros are calling on Congress to increase the estate tax.

In a joint statement Tuesday, Buffett, Soros and more than 20 other wealthy individuals asked Congress to lower the estate tax's per-person exemption to $2 million from $5.12 million and to raise the top rate to more than 45 percent from 35 percent.

An estate tax structured this way will "raise significant revenue to reduce the deficit and fund vital services, will only be paid by the top one percent of estates, will raise more from the wealthiest estates" and will simplify compliance, said the statement. It also was signed by John Bogle, founder of mutual fund company Vanguard Group Inc., and former President Jimmy Carter.

The renewed push for increasing the estate tax faces significant opposition in Congress, where Senate Democrats including Max Baucus of Montana and Mark Pryor of Arkansas have joined Republicans to support the current estate tax parameters.

There's probably enough support among Democrats to maintain the existing estate tax parameters, said Carolyn Lee, senior director of tax policy at the National Association of Manufacturers in Washington, which supports existing levels.

"We think that family-held and multigenerational businesses are important," she said. "It's part of the American way of life."

Changes to the estate tax are among the more than $600 billion in automatic spending cuts and tax increases scheduled to start in January -- the "fiscal cliff."

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If Congress does nothing, the amount one could exempt from the estate tax would drop to $1 million, and the rate would increase to 55 percent. Obama wants to reinstate the 2009 levels, which include a $3.5 million exemption and a 45 percent top rate. Compared with continuing current policies, Obama's plan would raise $119 billion over the next decade, according to his budget proposal.