Treasury Secretary Steven Mnuchin Steven Terner MnuchinHillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars Treasury: Trump's payroll tax deferral won't hurt Social Security Treasury sanctions individuals, groups tied to Russian malign influence activities MORE on Sunday doubled down on comments that 90 percent of Americans will be able to file their taxes on a postcard under Republican legislation.

"Over 90 percent of Americans are going to fill out taxes on that postcard or a virtual electronic postcard. This is about simplifying taxes and simplifying the business systems," Mnuchin told host Chris Wallace on "Fox News Sunday."

"So there will always be people who complain that are losing tax breaks, but this is about making it simple for the American public," he added.

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Wallace pressed him on claim, however, pointing to changes to the bill.

“I want to press on that because that’s a new number. I heard that originally, but you’re still saying over 90 percent of Americans would be able to file on a postcard?” Wallace asked.

"Absolutely, they will take the standard deduction and that is what they will file," Mnuchin responded.

The Treasury secretary added that the Trump administration is already in the process "of designing new forms so Americans don’t have thousands of pages of tax forms."

Republicans are on the verge of passing legislation to reform the tax code for the first time in 30 years, which would give President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE his first major legislative win.

Senate Majority Whip John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas) said on Sunday that he expects the upper chamber to pass the measure on Tuesday.