by JOHN D. MCKINNON, The Wall Street Journal

Buried within the mass of tax and spending provisions known as the fiscal cliff is a problem that could cause grief for taxpayers and the Internal Revenue Service.

It is the alternative minimum tax, a provision adopted in the 1960s to make sure the very wealthiest didn’t avoid taxes by accumulating too many deductions and credits. It wasn’t indexed for inflation, and Congress has repeatedly passed an annual exemption to protect middle-class families from the tax.

Congress hasn’t passed that extension for this year. And with talks over avoiding the fiscal cliff stalled, it may not pass one. If it doesn’t, the tax will hit almost 30 million additional households, and could hit some couples making as little as $45,000 and individuals making as little as $33,750, according to the IRS. Just four million households had to pay the tax in 2011.

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