Hunter Biden is suing the Internal Revenue Service (IRS) after allegations that its agents illegally released his tax affairs.
The US president’s son, 53, said that his tax details were shared by two IRS agents in congressional hearings and media interviews in an “assault” on his right to confidentiality.
Mr Biden is seeking $1,000 (£800) for each unauthorised disclosure and associated legal fees.
The case centres on disclosures by two agents who were involved in an investigation of Mr Biden’s taxes and alleged that his case was being mismanaged by the US Department of Justice.
The agents, Greg Shapley and Joe Ziegler, said that they were acting as whistleblowers and accused the department of “slow-walking” the investigation in testimony before Congress.
The Department of Justice has emphatically denied any political interference in the case.
Mr Biden’s lawsuit argues the agents “targeted and sought to embarrass” him and the tax agency failed to protect his private records.
Whistleblowers are “supposed to uncover government misconduct”, it stated, not give their “opinion about the alleged wrongdoing of a private person”.
It added that whistleblower protections do not include divulging personal tax details and other confidential information to the press or in testimony before Congress.
The lawsuit is Mr Biden’s most aggressive move yet in his ongoing legal fight with the Department of Justice.
The department brought criminal charges against the president’s son last week in an historic first.
It followed the collapse of a plea deal in which Mr Biden would have pled guilty to minor tax offences and avoided prosecution on a gun charge.
Prosecutors said that Mr Biden earned taxable income of at least $1.5 million (£1.21 million) in each of the calendar years 2017 and 2018.
He did not pay income tax in those years despite owing more than $100,000.
They also said that he unlawfully possessed a firearm for 11 days in 2018 while using drugs.
He faces a possible trial next year on three federal gun charges filed last week.
He could still face prosecution for his alleged tax crimes.
Impeachment inquiry launched
Mr Biden’s case has become a political touchstone for Republicans in Congress, who have pursued their own inquiries into his business deals.
They have accused him of wrongdoing and accused the US president of profiting from or influencing his ventures.
They have yet to provide substantive supporting evidence, but have launched an impeachment inquiry into the president to bolster their investigative powers.
In an angry missive to a Republican congressman on Monday, Mr Biden’s lawyer Abbe Lowell said their improper disclosures of his client’s 2018 finances did not account for tax he eventually paid.
Mr Biden paid more than $900,000 to the IRS to resolve their investigation, he said.
His lawyers and accountants now believe he overpaid and is owed a refund.
The IRS and lawyers for the two IRS agents did not immediately respond to a request for comment.
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