An Internal Revenue Service official has filed a whistleblower complaint reporting that he was told that at least one Treasury Department political appointee attempted to improperly interfere with the annual audit of the president or vice president's tax returns, according to multiple people familiar with the document.

Trump administration officials dismissed the whistleblower's complaint as flimsy because it is based on conversations with other government officials.

But congressional Democrats were alarmed by the complaint, now circulating on Capitol Hill, and flagged it in a federal court filing. They are also discussing whether to make it public.

The details of the IRS complaint follow news of a separate, explosive whistleblower complaint filed in August by a member of the intelligence community.

That complaint revealed Donald Trump's request of Ukrainian leaders to investigate former vice president Joe Biden, a political rival. It has spurred an impeachment probe on Capitol Hill.

The Democrat challengers to Trump in 2020 Show all 25 1 /25 The Democrat challengers to Trump in 2020 The Democrat challengers to Trump in 2020 Bernie Sanders The Vermont senator has launched a second bid for president after losing out to Hilary Clinton in the 2016 Democratic primaries. He is running on a similar platform of democratic socialist reform Getty The Democrat challengers to Trump in 2020 Joe Biden The former vice president recently faced scrutiny for inappropriate touching of women, but was thought to deal with the criticism well and has since maintained a front runner status in national polling EPA The Democrat challengers to Trump in 2020 Elizabeth Warren The Massachusetts senator is a progressive Democrat, and a major supporter of regulating Wall Street Reuters The Democrat challengers to Trump in 2020 Amy Klobuchar Klobuchar is a Minnesota senator who earned praise for her contribution to the Brett Kavanaugh hearings Getty The Democrat challengers to Trump in 2020 Michael Bloomberg Michael Bloomberg, a late addition to the 2020 race, announced his candidacy after months of speculation in November. He has launched a massive ad-buying campaign and issued an apology for the controversial "stop and frisk" programme that adversely impacted minority communities in New York City when he was mayor Getty Images The Democrat challengers to Trump in 2020 Tulsi Gabbard The Hawaii congresswoman announced her candidacy in January, but has faced tough questions on her past comments on LGBT+ rights and her stance on Syrian President Bashar al-Assad Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Pete Buttigieg The centrist Indiana mayor and war veteran would be the first openly LGBT+ president in American history Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Deval Patrick The former Massachusetts governor launched a late 2020 candidacy and received very little reception. With just a few short months until the first voters flock to the polls, the former governor is running as a centrist and believes he can unite the party's various voting blocs AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Beto O'Rourke The former Texas congressman formally launched his bid for the presidency in March. He ran on a progressive platform, stating that the US is driven by "gross differences in opportunity and outcome" AP The Democrat challengers to Trump in 2020 DROPPED OUT: Kamala Harris The former California attorney general was introduced to the national stage during Jeff Sessions’ testimony. She has endorsed Medicare-for-all and proposed a major tax-credit for the middle class AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Bill De Blasio The New York mayor announced his bid on 16 May 2019. He emerged in 2013 as a leading voice in the left wing of his party but struggled to build a national profile and has suffered a number of political setbacks in his time as mayor AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Steve Bullock The Montana governor announced his bid on 14 May. He stated "We need to defeat Donald Trump in 2020 and defeat the corrupt system that lets campaign money drown out the people's voice, so we can finally make good on the promise of a fair shot for everyone." He also highlighted the fact that he won the governor's seat in a red [Republican] state Reuters The Democrat challengers to Trump in 2020 DROPPED OUT: Cory Booker The New Jersey Senator has focused on restoring kindness and civility in American politics throughout his campaign, though he has failed to secure the same level of support and fundraising as several other senators running for the White House in 2020 Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Wayne Messam Mayor of the city of Miramar in the Miami metropolitan area, Wayne Messam said he intended to run on a progressive platform against the "broken" federal government. He favours gun regulations and was a signatory to a letter from some 400 mayors condemning President Trump's withdrawal from the Paris Climate Accord Vice News The Democrat challengers to Trump in 2020 DROPPED OUT: Kirsten Gillibrand The New York Senator formally announced her presidential bid in January, saying that “healthcare should be a right, not a privilege” Getty The Democrat challengers to Trump in 2020 DROPPED OUT: John Delaney The Maryland congressman was the first to launch his bid for presidency, making the announcement in 2017 AP The Democrat challengers to Trump in 2020 DROPPED OUT: Andrew Yang The entrepreneur announced his presidential candidacy by pledging that he would introduce a universal basic income of $1,000 a month to every American over the age of 18 Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Julian Castro The former San Antonio mayor announced his candidacy in January and said that his running has a “special meaning” for the Latino community in the US Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Marianne Williamson The author and spiritual adviser has announced her intention to run for president. She had previously run for congress as an independent in 2014 but was unsuccessful Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Eric Swalwell One of the younger candidates, Swalwell has served on multiple committees in the House of Representatives. He intended to make gun control central to his campaign but dropped out after his team said it was clear there was no path to victory Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Seth Moulton A Massachusetts congressman, Moulton is a former US soldier who is best known for trying to stop Nancy Pelosi from becoming speaker of the house. He dropped out of the race after not polling well in key states Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Jay Inslee Inslee has been governor of Washington since 2013. His bid was centred around climate change AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: John Hickenlooper The former governor of Colorado aimed to sell himself as an effective leader who was open to compromise, but failed to make a splash on the national stage Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Tim Ryan Ohio representative Tim Ryan ran on a campaign that hinged on his working class roots, though his messaging did not appear to resonate with voters Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Tom Steyer Democratic presidential hopeful billionaire and philanthropist Tom Steyer is a longtime Democratic donor AFP/Getty

The IRS complaint has come amid the escalating legal battle between the Treasury Department and House Democrats over the release of Mr Trump's tax returns. Part of that inquiry from Democrats is over how the IRS conducts its annual audit of the president and vice president's tax returns. That process is supposed to be walled off from political appointees and interference.

That was the focus of the whistleblower complaint. The people briefed on its contents said, for the first time, that the complaint pertained to allegations of interference in the audit process by at least one Treasury Department official. They also said, for the first time, that the complaint revealed that the whistleblower is a career IRS official.

The existence of a whistleblower complaint was revealed in a court filing several months ago, but little about it had become public.

The whistleblower's account focuses on the integrity of the government's system for auditing the president's and vice president's tax returns.

Mr Trump has broken decades of precedent by refusing to publicly release his tax returns. Democrats filed a lawsuit earlier this year demanding the disclosure of those filings, invoking a federal law designed to give Congress access to any tax return.

The IRS complaint has received less attention but has divided government officials.

Two administration officials have described the complaint as hearsay and suggested it was politically motivated, but they spoke on the condition of anonymity because of the sensitivity of the matter.

Democrats who have reviewed it regard it as a deeply significant allegation that, if true, suggests that political appointees may have tried to interfere with the government audit process, which was set up to be insulated from political pressures.

Key parts of the complaint remain under wraps in part because of strict privacy laws that prevent the disclosure of any details related to the filing of tax returns.

People who described the complaint spoke on the condition of anonymity.

Representative Richard Neal, the chairman of the House Ways and Means Committee who received the whistleblower's complaint in July, said in court filings this summer that the complaint contains credible evidence of "potential 'inappropriate efforts to influence' the audit programme."

Mr Neal has also said the complaint raises "serious and urgent concerns."

The whistleblower, a career official at the IRS, confirmed in an interview with The Washington Post this week that he had filed a formal complaint and sent it to the tax committee chairs in both houses of Congress, including senator Charles Grassley, and to the Treasury Department inspector general for tax administration on 29 July.

The whistleblower would not comment on the substance of the complaint itself but focused on the importance of protecting those who come forward to disclose problems in government.

Mr Trump has closely guarded any details of his tax returns, refusing to release them during his presidential campaign and throughout his presidency. He has given a variety of reasons for refusing to release the returns, often saying they are under audit and therefore should remain private.

Mike Pence, the vice president, has also not made any of his recent tax returns public.

Mr Neal has not revealed whether the whistleblower complaint is about Mr Trump or Mr Pence, but he said in an August court filing that the allegations "cast doubt" on the Trump administration's contention that there is no reason for concern that IRS employees could face interference when auditing a president's tax returns.

'Hey president Trump, my wife and I just released 10 years!': Bernie Sanders calls on Donald Trump to reveal tax returns

It is very unusual for political appointees at Treasury to ask IRS career staff about the status of an individual's audit, according to legal experts and former IRS officials.

"Nobody at the Treasury Department should be calling to find out the status of anybody's audit," said John Koskinen, who served as IRS commissioner under both Mr Trump and Barack Obama.

"For a Treasury official to call a career person - even just for information - seems to me highly inappropriate, even if it's just checking in on how it's going."

The Post has been unable to verify the allegation in the whistleblower's complaint of improper communication between Treasury and IRS on the tax audit programme.

A spokesperson for the Treasury Department did not comment on details of the complaint.

Steven Mnuchin, the treasury secretary, previously told Mr Neal he forwarded the complaint to the inspector general's office.

A spokesperson for Mr Neal refused to share any details about the substance of the complaint, citing taxpayer protection rules.

Michael Zona, a spokesperson for Mr Grassley, also declined to comment, saying the senator does not discuss such confidential complaints.

However, the top Democrat on the committee Mr Grassley leads called for the panel to look into the complaint immediately.

"It would be negligent for the Finance Committee to fail to investigate a whistleblower's allegations of political interference," senator Ron Wyden said. "A bipartisan committee effort to get to the bottom of this should have been started months ago."

James Jackson, a deputy inspector general at the Treasury Department, said in September when asked about the whistleblower complaint at a congressional hearing: "We can't confirm or deny that we may or may not be doing anything. I can tell you, though, that anytime we get any kind of allegation in this world, in this realm, we investigate it aggressively."

Mr Jackson added: "We are not aware of any misconduct."

In his interview with The Post, the whistleblower dismissed the contention of critics that the complaint was uncorroborated.

"That's what investigations are for," he said.

He also denied his action was politically motivated.

"Anyone who knows me knows I would not hesitate to do the same, as would most career IRS public servants, regardless of any political preference," he said.

"I take very seriously the duty of career civil servants to act with integrity and perform our duties impartially, even at the risk that someone will make a charge of bias."

The whistleblower also castigated public officials who he said were making federal employees fearful of reporting wrongdoing. Mr Trump has in recent days said he wants to know the identity of the whistleblower in the Ukraine case.

Donald Trump 'will never release tax returns' claims White House official Mick Mulvaney

"I steadfastly refuse to discuss the substance or details of the complaint, but I have some legitimate concerns about reckless statements being made about whistleblowers," he said.

He said such statements "attack the messenger when the focus should be on the facts that were presented. I am concerned also by the relative silence of people who should be repudiating these dangerous attacks in the strongest terms."

Mr Neal told Bloomberg he is consulting with legal counsel about whether to release the whistleblower complaint.

The chairman has "been almost entirely silent about the whole matter" related to the whistleblower in private meetings of the Democrats on the Ways and Means Committee, according to one lawmaker who spoke on the condition of anonymity to discuss internal deliberations.

Legal experts and former government officials expressed alarm at the prospect of interference from political appointees with audits conducted by career IRS staff.

The tax returns of the president and vice president must be kept "at all times" in an orange folder and locked in a secure drawer or cabinet when the appointed IRS examiner is not with the documents, according to the IRS's manual.

"It's very important that enforcement matters, including audits, be handled independently by the IRS," said Mark W Everson, who served as IRS commissioner under George W Bush.

The mandatory audit programme refers only to the audit of the president and vice president, said Mark Matthews, who was a deputy IRS commissioner under Mr Bush and is now a partner at the firm Caplin & Drysdale. Those audits are viewed only by a small number of senior career IRS staff, Mr Matthews said.

The president's tax returns have already produced divisions between political appointees in the Treasury Department and officials at the IRS.

In May, The Post obtained a 10-page memo written by an attorney in the IRS Office of the Chief Counsel finding the administration had to turn over a president's returns if requested by Congress, unless the president invokes executive privilege.

The Treasury Department has denied Congress' request for the returns, but the White House has not invoked executive privilege.

In April, Mr Mnuchin also revealed that department attorneys consulted with the White House general counsel's office about the potential release of Mr Trump's tax returns before they were formally requested by House Democrats.

Mr Mnuchin, who said he was not involved in those conversations, said the communication between Treasury and White House attorneys was "informational" and that Treasury officials did not ask the White House for permission about whether to release the returns.

The whistleblower said that Treasury investigators, and presumably the inspector general, were aware of his complaint.

"I brought my concerns to my supervisors, who advised me to report the matter to the appropriate people with investigatory authority," he told The Post.

David Barnes, a spokesperson for the Treasury inspector general, declined to comment.

The whistleblower complaint was first disclosed by Mr Neal as part of his lawsuit against the Trump administration seeking six years of the president's tax returns, which the administration refused to turn over despite a 1924 law explicitly giving Congress the authority to obtain them.

Mr Neal told a federal court this summer that House Democrats had received an unsolicited message from a federal employee "setting forth credible allegations of 'evidence of possible misconduct' - specifically, potential 'inappropriate efforts to influence' the mandatory audit programme."