– An Internal Revenue Service (IRS) 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's 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 President Donald Trump's request of Ukranian leaders to investigate former Vice President Joe Biden, a political rival. It has spurred an impeachment probe on Capitol Hill.

The IRS complaint has come amid the escalating legal battle between the Treasury Department and House Democrats over the release of Trump's tax returns. Part of that inquiry from Democrats is over how the IRS conducts its annual audit of the president's 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.

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.

Rep. Richard Neal, D-Mass., 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 program." Neal has also said the complaint raises "serious and urgent concerns."

The whistleblower 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 Sen. Charles Grassley, R-Iowa, and to the Treasury Department Inspector General for Tax Administration on July 29.

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.

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. Vice President Mike Pence also has not made public any of his recent tax returns.

Neal has not revealed whether the whistleblower complaint is about Trump or 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.

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 Trump and President 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."

A spokesman for the Treasury Department did not comment on details of the complaint. Treasury Secretary Steven Mnuchin previously told Neal he forwarded the complaint to the inspector general's office.