Sen. Ron Wyden (Ore.), the top Democrat on the Senate Finance Committee, says that the FBI hasn't shared with Democrats on the panel the documents it's providing to committee Republicans as part of a probe into the Obama administration. 

Wyden sent a letter on Monday to FBI Director Christopher Wray saying that he is "deeply concerned" the bureau is violating its own policies and "succumbing to political pressure from Republicans to damage the Democratic presidential candidate," former Vice President Joe Biden. 

Wyden pointed to an Aug. 7 letter the FBI sent to the Senate Finance and the Homeland Security and Governmental Affairs panels providing an "update," on its compliance with the GOP investigations. The letter, according to Wyden, detailed documents given to the committees and the ability to review other information.  

"Based on this letter, it is evident that not only has most of the requested Crossfire Hurricane information that has been provided to the committees not been provided to the ranking members and their staffs, but Democrats were not informed of its existence," Wyden wrote in the letter, which was obtained by The Hill. 

The FBI, in a statement, said that it was working to provide the Senate committees with requested materials and "the same access is being provided to members of the majority and minority and their respective staffs." Asked if it was suggesting Wyden's letter wasn't an accurate description of interactions between the bureau and minority committee staff, the FBI declined to comment beyond the statement.

Wyden, in his letter, pointed out several instances ranging from the end of June through the end of July where the FBI either provided documents to committee Republicans related to their investigations or gave the GOP senators and staff the ability to review documents, but without informing Democrats of the documents or giving the same chance to review the information. 

"Providing documents to committee majorities without disclosure to the minority is unacceptable. Providing access to documents for review by Republican staffers without notice to, or inclusion of, Democratic staff is also unacceptable," Wyden wrote. 

He indicated in his letter that he had spoken with the FBI about how to address the issue going forward but wants to know why Democrats were excluded in recent weeks to begin with. 

He's also asking Wray to indicate if he or anyone on his staff made the decision to exclude Democrats, if the FBI has provided more documents to the GOP senators and if Democrats have been excluded from that, and how the FBI would ensure that both Republicans and Democrats on the committee had access to documents going forward. 

Asked if the majority on the committee is required by Senate rules to alert Democrats on the panel when they get documents or have the opportunity to review them so they would have the same access, a spokesman for Senate Finance Committee Chairman Chuck Grassley (R-Iowa) argued that was a decision for the FBI.

"In this case, it was the FBI that provided an in camera review of its documents. The FBI would determine who it grants access to in camera reviews," the spokesperson added.

Wyden's letter is the latest example of tensions around the Republican probes, which Democrats worry will inadvertently spread Russian misinformation. 

Grassley and Sen. Ron Johnson (R-Wis.), who chairs the Homeland Security and Governmental Affairs Committee, are months into two wide-reaching investigations.

One involves the Obama-era State Department, Obama-era Ukraine policy including work done by Biden, Biden's son Hunter Biden and any contact between the Obama administration and his associates or Burisma Holdings, where Hunter Biden was on the board.

The second is wide-ranging and broadly covers the transition process between the Obama and Trump administrations, but delves into everything from the FBI’s investigation into the Trump campaign and Russian election meddling and its offshoots to leaks from the early days of Trump’s presidency.

Johnson subpoenaed the FBI for documents last week as part of the second investigation, marking the first time he's used the broad subpoena authority given to him by Republicans on the panel in June. 

Johnson said he issued the subpoena — after receiving authorization at a committee meeting in June — because he "finally ran out of patience."

"This is ridiculous," Johnson said during an interview with Fox News last week. "I'm done fooling around."

—Updated at 12:58 p.m.