Two economists say that a preferential capital gains rate helped 400 of the wealthiest families.
Democrats may raise the debt ceiling using a fast-track process that bypasses the filibuster.
For those who want the tax break, the proposal lengthens the period investment funds must hold assets from three to five years.
In some cases, high-earning taxpayers would see a tax cut if the tax break were eliminated, according to the Tax Foundation.
The plan raises the top rate for taxing capital gains to 25% from 20% under current law.
The IRS also sent about $3.5 billion worth of stimulus checks to deceased individuals.
Taxes are emerging as a particularly contentious issue as lawmakers keep an eye on next year's midterm elections.
Democrats say lax rules have allowed companies to shift profits and jobs outside the U.S. for decades.
Democrats are weighing the option of bypassing the usual committee voting practice.
Income declined while government subsidies wiped tax liabilities during the pandemic year.