Sarah Huckabee Sanders says today is a 'huge day' ahead of tax bill vote that will hugely benefit America's wealthiest

White House Press Secretary Sarah Sanders has said it's going to be a "huge day", with both the Senate and House of Representatives expected to vote on the Republicans' tax bill.

Speaking on the show Fox & Friends, Ms Sanders said, "Today is a huge day, not just for the White House, not just for Congress but most importantly for America."

She added that middle-class Americans will "see the biggest benefit out of this tax package" - even though multiple analyses show the plan will disproportionately benefit the wealthy.

Ms Sanders also criticised Democrats for not participating in the process to reform the US tax code.

"This is a president who would’ve been happy to take their call and certainly happy to have their vote, to help Americans have more money in their paychecks, more money in their pockets, more money for businesses to reinvest in this country," Ms Sanders said.

In early December, the Senate passed its initial tax plan in a late-night vote with no Democratic support and one Republican defection, Tennessee Senator Bob Corker.

On Tuesday, the House and Senate plan to vote again on a final tax bill, which has undergone changes in the reconciliation process between the two chambers of Congress.

Mr Corker has since said that he will support the final tax bill.

Passage in both chambers appears all but certain.

"Congress is standing at the doorstep of an historic opportunity," Senate Majority Leader Mitch McConnell said on the Senate floor.

Republicans assert that the package of tax cuts for corporations, small businesses and individuals will boost economic and job growth.

"This is about expanding opportunities for people who are striving to make the most of their lives," House Speaker Paul Ryan said at a news conference.