The US House of Representatives has passed a massive tax bill that makes permanent and enhances tax credits to aid business research and development, the working poor, children and other temporary tax breaks.
The measure, passed by a vote of 318-109 in the Republican-led House with some support from Democrats on Thursday, is expected to increase US deficits by $US622 billion ($A863 billion) over 10 years.
Another $US58 billion in tax breaks are part of a $US1.1 trillion spending bill that funds federal government agencies through September 30, 2016, and lifts a four-decade-old ban on US crude oil exports.
The House is expected to vote separately on the spending bill on Friday.
Senior Senate aides have said the two measures, part of a bipartisan deal that would avert a shutdown, would likely be combined in that chamber and considered in a single vote on Friday.
House Democratic Leader Nancy Pelosi said she is not confident that enough Democrats will support the massive government funding bill to ensure its passage, although she plans to vote for the must-pass legislation.
Democratic votes are likely needed given opposition from some conservative Republicans.
"We have serious unease in our caucus," Pelosi told reporters at a news conference, adding that a provision to lift the ban on exporting US crude oil is the top obstacle in gaining enough Democrats' support.
The government last shut down in 2013 for more than two weeks due to a fight in Congress over Republican opposition to President Barack Obama's signature healthcare law, known as Obamacare.
