House Democrats looking to spare millions of middle-class families from the expensive bite of the alternative minimum tax are considering adding a surcharge of 4 percent or more to the tax bills of the nation's wealthiest households.

The alternative minimum tax is a parallel tax structure created in 1969 to nab 155 super-rich tax filers who had been able to wipe out their tax bills using loopholes and deductions. Under AMT rules, taxpayers must calculate their taxes twice -- once using normal deductions and tax rates and once using special AMT deductions and rates -- and pay the higher figure.

Republicans generally oppose new taxes on the wealthy, saying they disproportionately affect small businesses, but are waiting to hear more before deciding whether to work with Democrats or offer their own plan to abolish the AMT.