Romney 's proposal also would do away with the federal Alternative Minimum Tax and direct Congress to make up for lost revenue by scrapping existing deductions.
The Wall Street Journal said the details of the plan revealed ahead of a Romney speech in Detroit on Friday would limit deductions enjoyed by upper-income Americans -- but was not specific about which deductions might be affected. Romney's proposal would reduce individual tax rates in all six brackets by 20 percent, making the top income tax rate 28 percent instead of 35 percent. Middle-income earners would pay 20 percent.
Romney aides told the Journal the tax plan was intended to be revenue neutral.
"The pain would be tilted more to upper-income people," Romney economic adviser Glenn Hubbard said.
In September, the former Massachusetts governor proposed a 59-point economic plan that called for cutting the U.S. corporate tax rate from 35 percent to 25 percent.
The Journal, citing data from the Tax Policy Center, said eliminating the Alternative Minimum Tax could reduce tax revenue by nearly $58 billion in 2012.
GOP presidential hopeful Rick Santorum also has proposed dropping the AMT and streamlining the tax code to just two tax brackets – 28 percent for wealthy taxpayers and 10 percent for the lowest income bracket. Former House Speaker Newt Gingrich proposed a 15 percent flat tax on all taxpayers.
The candidates meet in a televised debate Wednesday night ahead of primaries Tuesday in Michigan and Arizona.