President Donald Trump showed no sign of softening his resistance to releasing his tax returns, with a spokesman saying he’s still "not inclined" to hand over the paperwork despite a Tuesday deadline set by Congress.

"The president is pretty clear. Once he’s out of audit, he will think about doing it. He’s not inclined to do so at this time," White House Deputy Press Secretary Hogan Gidley told FOX News.

The Treasury Department had until close of business Tuesday to respond to a second request from House Ways and Means Chairman Richard Neal to release the past six years of Trump’s personal and business tax returns

House Democrats are locked in a political battle with Treasury over whether Congress can legally obtain the president’s tax returns. Democrats say the law is on their side. The administration says the request is an illegal violation of Trump’s privacy.

The tax-return battle is just one front in Trump’s war against Democrats’ investigations of his conduct. On Monday, Trump and the Trump Organization asked a court to block a congressional subpoena seeking business records from his longtime accounting firm Mazars USA LLP.

Neal first asked for the tax returns April 3, citing a 1924 law that allows the chairmen of the congressional tax committees to view the returns of any taxpayer. The Massachusetts Democrat first asked for the documents by April 10. On that day, Treasury Secretary Steven Mnuchin said he was still reviewing the request and wanted to consult with the Justice Department if the Democrat’s demand is legal. Neal extended the deadline to Tuesday.

Mnuchin has said the Democrat’s request could be “an abuse of authority” and could “set a dangerous precedent.” William Consovoy, one of Trump’s attorneys, has argued that Neal’s request doesn’t have a legitimate purpose and flouts fundamental constitutional constraints. Trump opposes the request.

"He turned over hundreds of pages of financial disclosure forms during the campaign," Gidley said. "Everyone knows he is a very successful billionaire."

Democrats want the returns to see if he has ties to foreign businesses and whether he cheated on his taxes. Trump has said he is worth more than US$10 billion. The Bloomberg Billionaire Index pegs his wealth at US$2.8 billion. They also want to see if he benefited from his 2017 tax overhaul.

Trump broke with 40 years of presidential-campaign precedent when he refused to release his tax returns as a candidate. He said he was under audit and that he would consider releasing them when the audits were complete. No law prevents the release of tax returns that are under audit.

Gidley told the network "there is nothing nefarious" in his returns.

Democrats are intensifying their probes into Trump’s behavior since the release of the Mueller report April 18. On Monday, House Judiciary Committee Chairman Jerrold Nadler subpoenaed former White House Counsel Don McGahn to testify about Trump’s request that he have Mueller fired.