A key Democratic senator on Monday disputed Treasury Secretary Steven Mnuchin's assertion that it is "very hard" not to chop taxes for the wealthy.
Sen. Heidi Heitkamp of North Dakota said Republicans could reduce the tax burden on the middle class without helping the rich.
"When you lower the upper tax ... rate from 39 to 35 and you take away the alternative minimum tax, of course this is going to spin to the rich," she told CNBC's "Squawk Box."
"But if you said look — when the secretary, Secretary Mnuchin said there's no way you can give a tax break to the middle class without advantaging the rich — that's not true. I could do a tax credit to just those earners," Heitkamp said.
The White House and congressional Republicans are crafting a tax-cut plan that they hope to pass this year. The framework calls for across-the-board income tax reductions, a cut to the corporate tax rate and the removal of some provisions like the alternative minimum tax and estate tax. It also doubles the standard deduction.
An independent analysis by the Tax Policy Center estimated the richest 1 percent would get more than half of the benefits under the plan. It could also increase the tax burden on 28 percent of middle-class workers over time, according to the analysis.
Last week, Mnuchin defended against criticism that the plan helps the wealthy more.
"The top 20 percent of the people pay 95 percent of the taxes," he said in an interview with Politico. "The top 10 percent of the people pay 81 percent of the taxes."
"So, when you're cutting taxes across the board, it's very hard not to give tax cuts to the wealthy with tax cuts to the middle class. The math, given how much you are collecting, is just hard to do," Mnuchin said.
Heitkamp on Monday called for a plan in which the "bulk" of, "if not all," of the tax decrease benefits the middle class.
The North Dakota Democrat is among the senators in her party up for re-election next year in a state President Donald Trump won in 2016. Trump has aimed to win support from those Democrats, though they appear reluctant to back the GOP plan.
Trump partly used a speech in North Dakota last month to try to rally Heitkamp's support for the tax plan.