According to three sources familiar with the matter, including a former Justice Department tax official, multiple Justice Department whistleblowers have approached Republican Sen. Chuck Grassley as part of his ongoing investigation into the Biden family's business practices.

The sources told CBS News that the whistleblower disclosures raised concerns about the Hunter Biden investigation, with allegations including "irregular management" of evidence and "standard investigative procedures not being followed," allegedly impeding the progress of the investigation.

Whistleblower: FBI Failed to Follow Procedure in Hunter Biden Probe

Whistleblowers claimed that during the FBI investigation, derogatory evidence about President Biden's son, Hunter Biden, was incorrectly designated as disinformation, although it could have been or had been verified. In some instances, they claimed that damaging evidence was placed in highly restricted systems, preventing other FBI investigators from evaluating it as part of their related work.

Some of the most recent leaks involve an FBI internal form called FD 1023. In a letter sent to FBI Director Christopher Wray and Attorney General Merrick Garland in early May, Grassley - who is now the ranking member of the Senate Budget Committee - and House Oversight Committee Chairman James Comer asked what, if any, information the FBI has regarding an alleged bribery scheme involving President Biden.

The White House accused the lawmakers of launching an "unjustified political attack."

In a letter to Wray and Garland, Republican legislators inquired about the FD-1023 form, an FBI internal document that, according to the lawmakers, describes "an alleged criminal conspiracy involving then-Vice President Biden and a foreign national involving the exchange of money for policy decisions."

A whistleblower provided information about the alleged scheme, and Comer issued a subpoena to Wray for the form. In response to the subpoena, Christopher Dunham, acting assistant director of the FBI Office of Congressional Affairs, stated in a letter to Comer dated May 10 that the FD-1023 is "a form used to record unverified reporting from a confidential human source."

Republicans are filing contempt charges against FBI Director Chris Wray after he failed to hand over an internal document proving President Joe Biden was involved in a criminal $5 million conspiracy with a foreign national.

Tuesday was the deadline for the agency to turn over an internal unclassified FD-1023 form that appears to detail an arrangement between then-Vice President Biden and a foreign national for the exchange of money in exchange for policy decisions.

The Republicans issued a subpoena on May 4 for the document initially brought to their attention by a "credible" whistleblower. Last week, they provided two additional terms that may be referenced in the document: 'June 30, 2020' and 'five million.'

Comer affirmed that he will continue to speak with Wray and Sen. Charles Grassley, R-Iowa, on Wednesday and that they will continue to discuss the FBI's response. In response, the FBI told DailyMail.com that it "remains committed" to cooperating with the committee "in good faith."

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IRS Whistleblower Gary Shapley

Recently, an IRS criminal investigator who has accused Justice Department officials of dragging their feet on a long-running investigation into President Joe Biden's son Hunter's tax affairs has severed communication with a key congressional committee amid questions about the veracity of his claims and his motivations for coming forward.

Gary Shapley, a former member of the IRS's criminal investigations division, revealed his identity in an interview with CBS News. Shapley testified in a confidential session before the House Ways and Means Committee. This committee has jurisdiction over the IRS and is managed by Republican Representative Jason Smith of Missouri.

The 14-year IRS veteran has cut off communication with the Senate Finance Committee, which governs the Internal Revenue Service, after his counsel met with committee representatives, even as he prepares to testify before the House panel.

Shapley has also canceled an interview with this committee, chaired by Oregon Democrat Senator Ron Wyden. Mark Lytle, a former federal prosecutor, is known to represent Shapley, according to a Finance Committee source who told The Independent that staffers from both the Republican and Democratic factions of the committee met with him.

Related Article: Biden Bribery Scheme: FBI Director Christopher Wray Urges To Speak With Comer Over Alleged $5 Million Payment