At left, House Oversight Chairman James Comer, a Republican from Kentucky, and, at right, Sen. Chuck Grassley, the ranking Republican on the Senate Budget Committee.
CNN  — 

Two top congressional Republicans are demanding internal FBI documents that an unnamed whistleblower claims will show then-Vice President Joe Biden was involved in a criminal scheme with a foreign national.

The unverified allegation, outlined in a new letter Wednesday, is the most explosive claim House Oversight Chairman James Comer and Senate Budget Committee ranking Republican member Chuck Grassley have lobbed at the now-president after both men have devoted significant time to investigating the Biden family’s business dealings.

Comer and Grassley alleged that a whistleblower claimed the Justice Department and FBI have an unclassified document “that describes an alleged criminal scheme involving then-Vice President Biden and a foreign national relating to the exchange of money for policy decisions. It has been alleged that the document includes a precise description of how the alleged criminal scheme was employed as well as its purpose,” according to a letter to both FBI Director Christopher Wray and Attorney General Merrick Garland.

“I guess basically we’ve got to wait to see what the document exactly says,” Grassley said in a Fox News interview. “The FBI needs to explain whether it’s accurate or not.”

Comer fired off a corresponding subpoena to the FBI calling for “all FD-1023 forms, including within any open, closed, or restricted access case files, created or modified in June 2020, containing the term ‘Biden,’ including all accompanying attachments and documents to those FD-1023 forms.”

The form in question, an FD-1023, is a document the FBI uses to memorialize meetings or information gathered from confidential sources. The document typically would include allegations from the source, including information not verified by the FBI.

“We believe the FBI possesses an unclassified internal document that includes very serious and detailed allegations implicating the current President of the United States. What we don’t know is what, if anything, the FBI has done to verify these claims or investigate further,” Grassley, an Iowa Republican, said in a news release, adding that the situation calls for congressional oversight.

White House spokesman for investigations Ian Sams tweeted a link to a Fox News clip discussing the Comer and Grassley announcement, saying that Republicans “prefer trafficking in innuendo.”

“For going on 5 years now, Republicans in Congress have been lobbing unfounded politically-motivated attacks against @POTUS without offering evidence for their claims. Or evidence of decisions influenced by anything other than U.S. interests,” Sams tweeted. “They prefer trafficking in innuendo.”

Ranking Democratic member of the House Oversight Committee, Rep. Jamie Raskin of Maryland, described the allegations as “recycling unsubstantiated claims floated by Senate Republicans.”

“Given Chair Comer’s commitment to ‘dismantle’ the FBI, it’s no surprise that he would rely on these unverified tips to attack President Biden in one more baseless partisan stunt,” Raskin said.

The Department of Justice declined to comment. The FBI said it received the letter and subpoena and declined further comment.

This story and headline have been updated with additional developments.