I.R.S. Official Is Said to Assert Political Meddling in Hunter Biden Inquiry

As Justice Department officials weigh whether to indict Hunter Biden, the investigator overseeing the Internal Revenue Service’s portion of the case has come forward with allegations of political favoritism in the inquiry that stand to add to the already fraught circumstances facing the department.

Congressional leaders learned of the investigator’s allegations on Wednesday when a lawyer sent them a letter asking for whistle-blower protections for his client. The letter stated that the unnamed client, identified as an “I.R.S. criminal supervisory special agent who has been overseeing” an ongoing and sensitive case, had knowledge of an array of misconduct including political meddling, according to a copy of the letter obtained by The New York Times.

While the letter from the lawyer, Mark D. Lytle, did not name Hunter Biden, Senate and House Republicans put out statements specifying that it was referring to him. The disclosure fed claims by congressional Republicans that a Justice Department run by the president’s political appointees could not be trusted to make a decision about his son based on the facts and law.

The letter said the client had information that would contradict sworn testimony to Congress from a senior political appointee, an apparent reference to Attorney General Merrick B. Garland, who has offered assurances that the U.S. attorney in Delaware, David C. Weiss, who was appointed by President Donald J. Trump, would be free to run the investigation.

In response, Hunter Biden’s criminal defense lawyer, Christopher Clark, fired back on Thursday, claiming that the I.R.S. supervisor broke the law by disclosing confidential taxpayer information and called on the Justice Department to investigate the supervisor. Mr. Clark said that the only way it was known that the supervisor’s complaints could be linked to the Hunter Biden investigation would be if the supervisor or his lawyer disclosed it, either of which, he said, would have been improper.

“It is a felony for an I.R.S. agent to improperly disclose information about an ongoing tax investigation,” said Mr. Clark, of the firm Clark Smith Villazor L.L.P.

“The I.R.S. 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,” Mr. Clark continued. “Unfortunately, that is what has happened and is happening here in an attempt to harm my client. It appears this I.R.S. agent has committed a crime, and had denied my client protections that are his right.”

The Justice Department has been weighing whether to charge Hunter Biden over two separate issues. One is his failure to meet filing deadlines for his 2016 and 2017 tax returns, and questions about whether he falsely claimed at least $30,000 in deductions for business expenses.

The other is whether he lied on a U.S. government form that he filled out to purchase a handgun in 2018. On the form, he answered that he was not using drugs — an assertion that prosecutors might be able to challenge based on his erratic behavior and possible witness accounts of his drug use around that period.

Legal experts said Congress and the executive branch — mainly the Justice Department — were likely to have vastly different views about whether the disclosure that the case in question involved Hunter Biden was legally problematic.

Congress, the experts said, has often taken the position that its oversight authority allows it to hear from whomever it wants about whatever it wants. On the other hand, the Justice Department was likely to see it as a potentially illegal disclosure about a continuing investigation. If Hunter Biden is indicted, the experts said, his lawyers could move to question the supervisor about whether he disclosed details about the investigation.

In a number of televised interviews, Mr. Lytle, the lawyer for the I.R.S. supervisor, declined to confirm that Hunter Biden was the subject of the investigation. Neither Mr. Lytle nor another lawyer representing the I.R.S. supervisor, Tristan Leavitt, responded to messages seeking comment about Mr. Clark’s assertions.

In a post on Twitter, Mr. Leavitt said, “Our client has an exemplary record and is making his disclosures to Congress the right way and for the right reasons.”

In any high-profile investigation, particularly those involving politically connected individuals, there are often disputes between agents, prosecutors, supervisors and senior Justice Department officials in Washington about how to conduct the inquiry and whether to bring charges.

I.R.S. and F.B.I. agents have complained for months that they have enough evidence to bring a case against Hunter Biden but that their superiors, who have to weigh factors like whether a less prominent person would be charged with a crime in the same circumstances, have yet to make decisions. Some tax lawyers at the Justice Department are said to be skeptical that there is enough evidence to bring a tax case.

Representative James R. Comer, Republican of Kentucky and the chairman of the House Oversight Committee, which has been pursuing an investigation into the Bidens’ business dealings, publicly said that the letter was about Hunter Biden, although Mr. Comer did not say how he knew that.

Mr. Comer said House Republicans would work to “hold accountable anyone in the Biden administration who may be covering up this criminal activity.”

“It’s deeply concerning that the Biden administration may be obstructing justice by blocking efforts to charge Hunter Biden for tax violations,” he said.

Mr. Comer and members of his committee this week have been reviewing reports that banks are required to file to the Treasury Department on any transaction that could potentially be a red flag for money laundering, including any cash transaction of more than $10,000.

The Treasury Department notes that such reports are “preliminary and unverified tip-and-lead information” that could result in a serious investigation or prove innocuous. Justice Department investigators have also examined a wide range of Hunter Biden’s business and financial dealings around the world but do not appear to be weighing charges related to those activities.