US President Donald Trump (File photo: AP)

WASHINGTON, July 2 (Xinhua) -- The Democrat-led House Ways and Means Committee on Tuesday sued the Treasury Department, the Internal Revenue Service (IRS) and their respective leaders, Steven Mnuchin and Charles Rettig, over their refusal to turn over President Donald Trump's tax returns, local media reported.

The panel's chairman, Richard Neal, filed the lawsuit using a little-known IRS provision known as section 6103(f) of the federal tax code, which allows the Chairmen of the House Ways and Means Committee and the Senate Finance Committee to request and obtain an individual's tax information for a legitimate legislative purpose, said the reports.

"In refusing to comply with the statute, Defendants have mounted an extraordinary attack on the authority of Congress to obtain information needed to conduct oversight of Treasury, the IRS, and the tax laws on behalf of the American people who participate in the nation's voluntary tax system," the lawsuit states.

The House Democrats argue that they need the returns to determine whether Trump has been compliant with federal tax law, and whether "the IRS's self-imposed policy of annually auditing the returns of sitting presidents is working properly, even though it has not been updated in decades."

Neal sent a request in April to the IRS seeking Trump's personal and business tax returns from 2013 to 2018. Treasury Secretary Steven Mnuchin rejected Neal's request in May, saying that it lacked a legitimate legislative purpose. Neal then issued subpoenas to Treasury and the IRS for Trump's tax returns, which Mnuchin also rejected.

Tax transparency has been in the spotlight after Trump rejected a decades-old tradition that presidents and White House hopefuls would make their tax returns public. Democrats have claimed that Trump's business dealings present a host of potential conflicts of interest that they can't understand without his tax information.

The lawsuit is long expected and could be a lengthy legal battle.