Another whistleblower complaint has been lodged, this one alleging "inappropriate efforts to influence" the mandatory IRS audit of President Donald Trump's and Vice President Mike Pence's tax returns.

In an August 8 letter to Treasury Secretary Steven Mnuchin, Rep. Richard Neal, the chairman of the House Ways and Means Committee, said his committee received credible allegations of "evidence of possible misconduct" from a federal employee in July.

Though the president is not required by law to release their tax returns, every president except Trump has voluntarily released their tax returns or a tax summary since 1974⁠.

Trump is also at the center of another whistleblower complaint, lodged in August, alleging that he repeatedly solicited foreign interference in the 2020 election from Ukraine. That complaint is the catalyst for a formal House impeachment inquiry into the president.

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Another whistleblower complaint alleges "possible misconduct" in an audit of President Donald Trump's taxes.

Rep. Richard Neal, the chairman of the House Ways and Means Committee, which has jurisdiction over taxes, tariffs, and other social-assistance programs, sent a letter to Treasury Secretary Steven Mnuchin on August 8 saying that a federal employee submitted "an unsolicited communication" on July 29 outlining allegations of "inappropriate efforts to influence" the mandatory IRS audit of Trump's and Vice President Mike Pence's tax returns.

In his letter, first widely reported this week, Neal described the whistleblower's allegations of "evidence of possible misconduct" as credible.

"This is a grave charge that appreciably heightens the Committee's concerns about the absence of appropriate safeguards as part of the mandatory audit program and whether statutory codification of such program or other remedial, legislative measures are warranted," he wrote.

Neal also wrote that his committee had "raised these concerns repeatedly" but that IRS Commissioner Charles Rettig had said they were "unfounded." Neal said the whistleblower's allegations "underscore the pressing need for complete and meaningful oversight" of the audit program.

Though the president is not required by law to release their tax returns, every president except Trump has voluntarily released their tax returns or a tax summary since 1974⁠.

He's repeatedly claimed that he cannot release them because they are under audit. The president's taxes are automatically audited by the IRS, and there is no rule or stipulation that says a person's tax returns cannot be released if they're under audit.

Read more: Trump is facing the biggest firestorm of his presidency because his own staffers blew the whistle on him

In July, Neal sued Mnuchin and Rettig to get ahold of six years' worth of Trump's tax returns. The court filing argued that under Section 6103 of the US tax code, the Treasury "shall furnish" any document requested by the House Ways and Means Committee chair.

The Treasury did not immediately respond to a request for comment.

It's unclear why Trump has not released his tax returns.

A New York Times investigation published a year ago suggested that he might have engaged in tax schemes, including fraud, during the 1990s.

The president is also at the center of another explosive whistleblower complaint filed by a US intelligence official in August. It was the catalyst for the House's impeachment inquiry into Trump.

At the heart of that complaint is a July 25 phone call Trump had with Ukrainian President Volodymyr Zelensky, in which the US president repeatedly pressed his Ukrainian counterpart to investigate former Vice President Joe Biden and his son ahead of the 2020 election.

Trump had ordered his administration to withhold a nearly $400 million military-aid package to Ukraine days before the phone call with Zelensky.

While the White House's notes on the call showed that Trump did not directly mention offering aid in exchange for Zelensky's assistance in investigating Biden, they confirmed that Trump brought up how the US does "a lot for Ukraine" right before asking Zelensky to do him a "favor" by investigating Biden and discrediting the former special counsel Robert Mueller's Russia probe.

The complaint alleged that Trump used the power of his office to "solicit interference from a foreign country" in the 2020 US election. His personal lawyer Rudy Giuliani is described as a "central figure in this effort," and it said Attorney General William Barr "appears to be involved as well."

Trump's handpicked acting spy chief, Joseph Maguire, also told the House Intelligence Committee last week that the White House's memo lined up with the complaint.

"Would you say that the whistleblower complaint is remarkably consistent with the transcript that was released?" Democratic Rep. Joaquin Castro of Texas asked Maguire.

"The whistleblower's complaint is in alignment with what was released yesterday by the president," Maguire replied.

He also emphasized that the complaint is credible — a conclusion shared by the intelligence community's inspector general — and that the whistleblower took all the right steps to report Trump's conduct.