At issue is a proposal by the supercommittee's Republicans to trade permanent cuts in income tax rates, with the top rate dropping to as little as 28 percent, for new limits on deductions, exclusions and other tax breaks. They estimate it would produce $300 billion to reduce the deficit.
The plan's principal author is Senator Pat Toomey, a Pennsylvania Republican who previously led the Club for Growth, a Washington anti-tax group.
Some conservative organizations are accusing Republicans of trying to hide tax increases through the Toomey plan.
"Closing tax loopholes is all well and good," said Americans for Tax Reform President Grover Norquist in an opinion article in Politico. "But doing so to raise revenues is just as much a tax hike as raising tax rates." He added, "Any congressman who wants to keep his promise to voters to oppose tax increases" must oppose the plan.
Many Republican lawmakers are also unhappy with the proposal. "We don't have a tax problem -- we have a spending problem," said Senator Jim DeMint, a South Carolina Republican. "For us to get lulled into 'how much to raise taxes' in this thing is foolish."
Senator Orrin Hatch, the top Republican on the tax-writing Finance Committee, said, "some of these loopholes really aren't loopholes." He said "they're important policy provisions, like the home interest mortgage deduction."
Republican supporters of the plan say they're trying to lock in lower income tax rates that will otherwise jump if, as is currently scheduled, former President George W. Bush's tax cuts expire at the end of next year. President Barack Obama opposes extending the Bush-era cuts for those earning more than $250,000, and Republicans are unlikely in the 2012 elections to win the Senate votes they would need to keep the tax cuts in effect.
'Biggest Tax Increase'
"What we're trying to do is avoid the biggest tax increase in the history of the country," Senator Charles Grassley, an Iowa Republican, said of Toomey's plan.
Toomey declined to comment other than to point to a Nov. 10 Wall Street Journal editorial quoting him as calling his proposal a "bitter pill" that's "justified to prevent the tax increase that's coming."