U.S. Treasury Secretary Steven Mnuchin warned Congress on Wednesday that the U.S. stock market could fall significantly if Congress do not pass tax reform.

"There is no question that the rally in the stock market has baked into it reasonably high expectations of us getting tax cuts and tax reform done," Mnuchin said with a Washington-based news website Politico in a podcast.

"There's no question in my mind that if we don't get it done you're going to see a reversal of a significant amount of these gains," he said.

The benchmark S&P 500 index has increased by about 20 percent since Donald Trump's win in the presidential election in November 2016, a fact Trump has mentioned frequently on the twitter.

Mnuchin's warning comes ahead of a vital vote in the Senate on Thursday on a budget resolution, which would pave the way for a tax cut worth up to 1.5 trillion U.S. dollars over 10 years.

The White House said in a statement that President Trump on Wednesday had a productive meeting about tax cuts and reform with the bipartisan group of Senators from the Senate Finance Committee.

"The group discussed the historic nature of tax cuts and reform, and stressed the urgent need to deliver tax relief for the middle class by cutting taxes and simplifying the burdensome tax code," the statement said.

The Trump administration, together with Congressional Republicans, last month released a unified framework for tax reform, which will cut tax rates for businesses and individuals while lacking details on how to consolidate fiscal position in face of big tax cuts.

Economists have criticized that wealthy people, not middle class, would be the big winners in the tax reform framework and the plan would also push up U.S. fiscal deficits and public debt.

A minority of middle-class households, particularly upper-middle-class households with several children living in high-tax states, would actually experience tax increases, according to Alan Viard, a resident scholar at the American Enterprise Institute.