U.S. President George W. Bush and Congress have pushed through that tax cut--the largest since the Reagan tax cut of 1981, no less--and you're seeing the happy result already right there on your paycheck. You may even be moved to say, Thank you, Uncle Sam, for cutting me a little slack. But for millions of Americans, Uncle Sam is doing a head fake: Washington fully intends to take back a large chunk of that tax cut. We're talking about something sneakier and much nastier: the Alternative Minimum Tax, or AMT. Put simply, the AMT is a tax regime that high-income people get thrown into when they take lots of deductions or enjoy a big jump in income, such as by exercising a heap of stock options. It's a kind of parallel tax universe that has very few deductions and forces you to pay far higher taxes in the future than you'd pay under the regular system. You lose the breaks for costs that Congress has consistently and vocally deemed break-worthy: things like property taxes, state and city income taxes, exemptions for children, the interest on home-equity loans--in fact, pretty much everything but mortgage interest and contributions to charity. What's most troubling and least understood about the AMT is the growth trajectory it's now on. According to a study by the Urban-Brookings Tax Policy Center--class warriors, please note, this is a liberal think tank--the number of Americans exiled to AMT land is about to explode. Indeed, by 2010, 33 million taxpayers, one-third of the total, will pay the AMT if the rules aren't changed. The AMT is even scarier when you look at this growth in dollar terms: By 2010, 55% of the income generated in this country will be subject to the AMT. If Washington does nothing, the AMT is on track to supplant the existing body of rules, rates, and deductions and become the dominant tax system in the U.S. INSET: Meet the Henrys.