Three sources, including a former Justice Department official, who are familiar with the issue, have confirmed that multiple Justice Department whistleblowers came forward as part of Republican Sen. Chuck Grassley’s ongoing investigation into Biden family business activities.

Sources told CBS News that the whistleblower disclosures raised questions about the Hunter Biden Investigation. Allegations included “irregular” handling of evidence, and the claim that “standard investigative procedures were not followed”, allegedly hindering progress.

Whistleblowers claimed that derogatory information about President Biden’s eldest son, Hunter Biden was incorrectly labelled as disinformation during the FBI investigation when it had been or could have already been verified. They claimed that in some cases derogatory information was stored in systems with high security levels, preventing other FBI investigators to review it as part of their work.

The FBI declined to comment on CBS News’ report. The FBI said it had no comment in response to CBS News.

Some of the most recent disclosures are related to an FBI internal form called an FD1023. In a May letter to FBI Director Christopher Wray, Attorney General Merrick Garrland, and House Oversight Committee Chair James Comer they asked what, if anything, information the FBI had about an alleged bribery plot involving President Biden. The White House at the time accused the lawmakers launching an unfounded political attack.

The GOP lawmakers wrote to Wray and Garland to ask about the FD-1023 document, a FBI internal document, which they claimed described “an alleged criminal plot involving Vice President Biden at the time and a foreigner relating to an exchange of money in return for policy decisions.”

Grassley, Comer and Wray said that a whistleblower provided information on the alleged scheme. Comer then issued a subpoena for Wray to provide the form.

The GOP lawmakers wrote that they thought the allegation was “specific” enough to determine if it is true. However, “it is unclear, if at all, what steps were taken to investigate this matter.”

Christopher Dunham wrote in a May 10 letter to Comer, as a response to the subpoena. He said that FD-1023 was a form used to record unverified reports from a confidential source.

Dunham wrote, “The FBI receives regular information from sources who have significant potential biases and motivations as well as knowledge. These include drug traffickers, organized crime members, or terrorists.”

Dunham said that it was crucial to the integrity and effectiveness of the criminal justice system, as well as the performance of our law-enforcement duties, that the FBI refrain from releasing information – including unverified or incomplete information – that could damage investigations.

“Your request for a FD-1023 that includes a precise’ description of an alleged criminal scheme risks the harms against which our confidentiality rules are designed to protect,” he continued.

“…We’d be happy to coordinate with your team to determine if we can accommodate your requests without violating law enforcement or national security obligations,” Dunhmam concludes his letter.

Ian Sams, the White House spokesperson for oversight and investigations, also said in response to the GOP letter, “For going on five years now, Republicans in Congress have been lobbing unfounded, unproven, politically-motivated attacks against the President and his family without offering evidence for their claims or evidence of decisions influenced by anything other than U.S. interests.”

He said, “If you want to know about President Biden’s finances, anyone can look at them: he offered a level of transparency unprecedented, by releasing 25 years worth of tax returns for the American public.”

CBS News was told by a GOP aide that Grassley previously scheduled a Wednesday call with Comer and Wray to discuss the subpoena of the FD-1023. The FBI told Comer on Tuesday that it would not release the document to the committee.

Comer released a statement stating, “While I am scheduled to speak with FBI Director Wray on Wednesday to discuss further his response, the Committee is clear in their intent to protect Congressional supervision authorities and will be taking steps now to hold the FBI director in contempt for refusing to obey a lawful Subpoena.”

In a separate statement, the FBI said that it had written Comer to say that they were “committed” to providing information in response to the Committee’s subpoena “in a format and environment that maintains confidentially and protects the integrity of FBI investigation and important security interests.”