The statement also notes that the government needs the money to both "fund vital services" and reduce the nation's budget deficit.
Under the current law, which expires at the end of the year, there is a $10 million exemption per couple. That "leaves too much revenue on the table," according to the statement.
(Read more: Buffett Expects 'Fiscal Cliff' Fix, but Not by December 31
Instead, Buffett and the other signers want a $4 million exemption, indexed to inflation, and a "graduated rate on the taxable estate over the exemption amount, beginning at 45 percent and rising on the largest fortunes."
The signers contend that only the top one percent of estates would have to pay taxes under their proposal.
(Read more: Warren Buffett's $250K Difference of Opinion with Obama)
This isn't a new cause for Buffett. Back in 2007, he went to Washington to appear before a Senate Finance Committee hearing on estate taxes. In his opening statement, Buffett said, "Dynastic wealth, the enemy of a meritocracy, is on the rise. Equality of opportunity has been on the decline. A progressive and meaningful estate tax is needed to curb the movement of a democracy toward a plutocracy."