Approximately a quarter of all taxpayers would eventually owe more to the IRS under the plan Congressional Republicans and President Donald Trump outlined this week, according to a preliminary analysis by the nonpartisan Tax Policy Center.

The new tax framework, which the White House rolled out Wednesday, is heavy on cuts for corporations, which tend to reward shareholders, as well as reductions for business owners. As a result, its benefits are skewed toward the wealthy—just over half of the cuts, which total $2.4 trillion over a decade, would go to the top 1 percent of taxpayers, who would see their after-tax incomes jump about 8.5 percent on average during the first year of the plan. In contrast, the middle 20 percent of taxpayers would enjoy just a 1.2 percent bump.

Of course, tax giveaways to millionaires are pretty much standard GOP policy fare. But the plan’s attempts to partly pay for itself could end up costing money for many families among the bottom 90 percent—which one has to imagine would make it politically toxic.

Households with six-figure incomes would be especially likely to see a hike, but working-class families could see their tax bills rise as well. By 2027, 30 percent of taxpayers earning between $50,000 and $150,000 and 60 percent of those making between $150,000 and $300,000 would owe more to the government. Meanwhile, nine in 10 members of the top 1 percent would get a tax cut.

The GOP’s framework is still missing key details, and a fully fleshed out version isn’t expected to emerge for weeks. As a result, the Tax Policy Center’s analysts made a number of assumptions about how the final legislation might look. Some are based on prior GOP proposals. For instance, it assumed that Republicans would seek to increase the Child Tax Credit by $500—in line with what the House GOP included in its campaign season tax plan.

Other assumptions may be a little more tenuous. The Republican framework says it will try to balance some of its corporate cuts by partially reducing the amount of interest from debt that companies can deduct. That could, in theory, raise a great deal of money. But because the plan doesn’t attach any specific numbers to that proposal, TPC leaves it out of their analysis. It’s also possible that Republicans will subject fewer families to the top 35 percent bracket than TPC assumes, which would spare them from increases.

On the other hand, TPC also generously assumes Republicans will leave in place what’s known as “head of household filing status,” which single parents use to reduce their tax burden. It’s currently unclear whether the Republican plan would eliminate it. If they do, even more families with modest incomes could end up owing extra.

Still, this first gloss does serve as an alarm of sorts about how a Republican plan aimed at letting corporations keep more of their profits could end up costing many ordinary Americans. Not counting the estate tax (which would disappear, much to the benefit of the families like the Waltons), TPC thinks the framework would raise taxes on individuals by $471 billion over a decade, while cutting them on businesses by $2.6 trillion. And it’s not exactly billionaires who are going to be shouldering the burden on families.

There are a few key features of the Republican framework that lead to the tax hikes that show up in TPC’s analysis. The party has talked about eliminating most itemized deductions—most importantly the one for state and local taxes, which would on its own raise $1.3 trillion, and could end up costing upper-middle-class households in the plan’s early years. That idea is already stoking a rebellion among Republican House members from blue states like New York and New Jersey that would be hit especially hard; it might not survive. Down the line, other, subtler parts of the plan could hit families’ pocketbooks. The framework would essentially replace personal exemptions, which are indexed for inflation, with a higher child tax credit, which is not, and would thus lose value over time. The plan would also slow the rate at which the thresholds for each tax bracket rise, meaning over time people would find themselves tumbling into a higher rates.

Again, TPC’s analysis is very preliminary. But this is a plan that’s been sold as a middle-class tax cut. For a good chunk of Americans, it could be just the opposite.