A Democrat-controlled US House of Representatives committee was poised to release six years of former US president Donald Trump's tax returns to the public on Friday in an extraordinary move days before Republicans take control of the chamber.

The release of Trump's returns for 2015 to 2020 will cap a multi-year battle between the former Republican president and Democratic lawmakers.

House Ways and Means Committee Chairman Richard Neal requested the returns in 2019, arguing that Congress needed to see them to determine if legislation on presidential returns was needed.

Trump, who took office in 2017, was the first presidential candidate in decades who did not release his taxes, and he sued the committee in an effort to keep them private. The Supreme Court ruled in November in the committee's favour.

In a report last week, the committee outlined its findings from its examination of the documents, saying the IRS broke its own rules by not auditing Trump for three out of four years while he was president.

Details released by the panel showed Trump paid no income tax in 2020, his final full year in office, despite millions of dollars in earnings from his sprawling business empire.

The records show Trump's income and tax liability fluctuated dramatically from 2015 through 2020, during his first presidential bid and subsequent term in office.

They show that Trump and his wife Melania claimed large deductions and losses and paid little or no income tax in several of those years.

Democrats were on a tight timeline to find a way to handle the returns once they obtained them, given that Republicans would take control of the House on Jan 3 after winning a slim margin in November's midterm elections.

Republicans have decried the quest for tax returns as politically motivated.

The Democrat-controlled House passed a bill before it left on its winter recess that would mandate the IRS to complete audits of presidents' tax filings within 90 days of their inauguration.