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Republicans say they want their tax code to give middle-class Americans a break, but some analysts are warning a few vulnerable groups may not get relief.

The biggest winners under the GOP tax plan, released on Thursday, are corporations and the rich, according to both the Institute on Taxation and Economic Policy and the Center for American Progress. The richest 1 percent of US households would receive 31 percent of the tax cut next year, the largest share among all income groups, the ITEP said.

The Tax Cuts and Jobs Act will likely benefit some low-wage and middle-class Americans, although the tax cuts will likely be meager for many households. The poorest 20 percent of Americans will receive an average annual tax reduction of $130 in 2018, or less than 1 percent of their income, while the richest 1 percent will see their taxes fall by 2.4 percent of their income, the ITEP estimated.

On top of that, the tax bill removes or caps several popular tax deductions, which may add to the hurdles some Americans face in managing their finances.

"A closer look at the details of this tax plan indicates that lawmakers are most serious about ensuring that they lower tax bills for the highest-earning households," Alan Essig, ITEP's executive director, said in a statement.

Critics say corporations would come out ahead because the proposal would slash the business tax rate to 20 percent from 35 percent. While the proposal maintains the top personal income tax rate of 39.6 percent, it would eventually eliminate the estate tax and the alternative minimum tax, which are levied on either wealthy or higher-income households, respectively.

To be sure, the House GOP tax plan is likely to evolve as lawmakers wrangle with the details and as special interests press for changes. It's also possible a tax reform bill could fizzle, even with Republicans controlling both chambers of Congress, as some provisions -- such as capping the popular mortgage interest deduction -- come under fire from lobbyists, lawmakers and consumers.

Read on to learn about the five types of taxpayers who might not benefit under the House GOP proposal.