IRS whistleblower has told Congress that Hunter Biden probe is being mishandled

A supervisor at the IRS has told lawmakers that he has information that suggests the Biden administration could be mishandling the investigation into President Joe Biden's son, Hunter Biden, sources familiar with the matter told ABC News.

In a letter to lawmakers obtained by ABC News, the lawyer for the IRS whistleblower says his client is an IRS criminal supervisory special agent "who has been overseeing the ongoing and sensitive investigation of a high-profile, controversial subject since early 2020 and would like to make protected whistleblower disclosures to Congress."

The letter does not name Hunter Biden specifically, but lawmakers have been made aware he is the "high profile, controversial" subject that the lawyer is referring to. In addition, while the letter refers to preferential treatment that Hunter Biden has allegedly received, there are no specific examples provided to support the accusations.

The letter says that "The protected disclosures: (1) contradict sworn testimony to Congress by a senior political appointee, (2) involve failure to mitigate clear conflicts of interest in the ultimate disposition of the case, and (3) detail examples of preferential treatment and politics improperly infecting decisions and protocols that would normally be followed by career law enforcement professionals in similar circumstances if the subject were not politically connected."

The lawyer for the whistleblower didn't immediately respond to ABC's request for comment. A spokesperson for DOJ declined to comment.

The Wall Street Journal first reported news of the letter.

"It's deeply concerning that the Biden Administration may be obstructing justice by blocking efforts to charge Hunter Biden for tax violations," House Oversight Committee Chair James Comer (R-Ky.), said in a statement.

"The House Committee on Oversight and Accountability has been following the Bidens' tangled web of complex corporate and financial records," said Comer, who was one of the recipients of the letter. "We've been wondering all along where the heck the DOJ and the IRS have been. Now it appears the Biden Administration may have been working overtime to prevent the Bidens from facing any consequences."

In a statement issued Thursday in response to the letter, Chris Clark, an attorney for Hunter Biden, said, "It appears this IRS agent has committed a crime" by disclosing information about his client.

"It is a felony for an IRS agent to improperly disclose information about an ongoing tax investigation," Clark said in the statement. "The IRS has incredible power, and abusing that power by targeting, embarrassing, or disclosing information about a private citizen's tax matters undermines Americans' faith in the federal government."

"Unfortunately, that is what has happened and is happening here in an attempt to harm my client," said Clark. "It appears this IRS agent has committed a crime and had denied my client protections that are his right."

White House officials are not commenting on the whistleblower claims, and instead referred questions to the Justice Department and IRS.

Federal authorities with the U.S. attorney's office in Delaware, led by U.S. Attorney David Weiss, a Trump-era appointee, have been investigating Hunter Biden since 2018, ABC News has previously reported.

ABC News' Lucien Bruggeman and Justin Gomez contributed to this report.