The person who filed a second whistleblower complaint against President Donald Trump works at the IRS, The Washington Post reported.

The complaint alleges "inappropriate efforts to influence" the agency's audit of Trump's tax returns, according to a court filing from the House Ways and Means Committee.

According to The Post, the person accused of trying to interfere with the audit is a political appointee at the Treasury Department.

"The president's and vice president's tax returns are kept in a top-secret vault," one Justice Department veteran told Insider. "It's code-word-protected, the whole nine yards, and not just anyone can get in there. There are very few people — the head of the Treasury, the head of the IRS — who have access."

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The person who filed a second whistleblower complaint against President Donald Trump is an IRS employee, The Washington Post reported on Thursday.

The complaint alleges "inappropriate efforts to influence" the agency's audit of Trump's tax returns, according to a court filing from the House Ways and Means Committee.

According to The Post, the person accused of trying to interfere with the audit is a political appointee at the Treasury Department.

There aren't many government officials who have access to the president's and vice president's tax documents, Jeffrey Cramer, a former federal prosecutor who spent 12 years at the Justice Department, told Insider.

"The president's and vice president's tax returns are kept in a top-secret vault," Cramer said. "It's code-word-protected, the whole nine yards, and not just anyone can get in there. There are very few people — the head of the Treasury, the head of the IRS — who have access."

Rep. Richard Neal, the chairman of the House Ways and Means Committee, wrote that he received a credible complaint from a whistleblower at the end of July. The panel is trying to obtain six year's worth of Trump's tax returns.

The president has repeatedly refused to release them, claiming they're under audit, even though there's no rule that says that people cannot disclose their returns on the basis of an audit.

Not much is known about the process of auditing a president. Rules governing it were tightened after President Richard Nixon was accused of influencing the process.

"One of the things that came out of Watergate was that he and his office had tried to use the IRS to go after political enemies," Patrick Cotter, a former federal prosecutor who was part of the team that convicted John Gotti, the Gambino crime family boss, told Insider.

In the wake of the scandal, Congress enacted a law making it a crime for any member of the executive branch to cause or terminate an IRS audit.

Because presidential candidates have voluntarily released records in the past several decades, the executive audit process has received little attention since Nixon.

But Neal argued in his filing that the existing guidelines are insufficient, because of the vast powers of the presidency, and that the president's tax records therefore need congressional oversight.

If Neal's demand is granted, he'll be given access to the president's tax records, which opponents believe could expose wrongdoing by Trump.

The Treasury Department has so far blocked Neal's request, arguing that the Massachusetts Democrat isn't seeking oversight for sound reasons but in an effort to damage the president's reputation.

Trump has been at the center of several financial scandals. The New York Times reported last year that Trump used a series of dubious tax schemes to shield a $400 million inheritance from the IRS.

And in September, Mother Jones published an investigation that found Trump might have fabricated a loan to avoid paying $50 million in income taxes.

The president has denied involvement in any financial wrongdoing.

Trump is also at the center of another whistleblower's complaint from a US intelligence official who alleges that he used a July 25 phone call with Ukraine's president to repeatedly pressure him to investigate former Vice President Joe Biden and his son. The complaint sparked a formal House impeachment inquiry into Trump last week.