The Treasury Department is complying with requests from GOP senators and has turned over highly sensitive information regarding Hunter Biden and his business associates to Republican senators who have asked for the materials, Yahoo News reported on Thursday.

According to the news outlet, a spokeswoman for Sen. Ron Wyden (D-Ore.), the top Democrat on the Finance Committee, said that the Treasury Department is "voluntarily cooperating" with the Senate Republicans' requests "at lightning speed."

"Agencies like the Treasury Department are rapidly complying with Senate Republican requests — no subpoenas necessary — and producing 'evidence' of questionable origin," the spokeswoman said.

For months now, Republican Sens. Chuck Grassley (Iowa), chairman of the Finance Committee, and Ron Johnson (Wis.) chairman of the Homeland Security and Governmental Affairs Committee, have been conducting an investigation into "potential conflicts of interest posed" by Biden's business dealings.

The two senators have been sending letters to numerous departments and agencies in Washington — including the State Department, the Treasury, the Justice Department, the FBI, the National Archives and the Secret Service — requesting information to aid their investigation.

According to Wyden, their requests to the Treasury Department have been met with cooperation. Yahoo News reports that Grassley and Johnson have sought "some of the most sensitive and closely held documents in all of federal law enforcement — highly confidential suspicious activity reports (SARs) filed by financial institutions with FinCEN, an agency of the Treasury that helps to police money laundering."

While it seems clear that some documents have been turned over in response to the senators' requests, it is not yet certain that SARs were among those documents.

The Treasury Department website notes that a financial institution is required to file a SAR after it deems an "initial detection of facts" constitutes one. Such constituting activities include cash transactions that exceed $10,000 or behavior that "might signal criminal activity."

A copy of the senators' letter to the Treasury Department, made available by Reuters, shows that Grassley and Johnson requested SARs and related documents pertaining to Biden, Burisma Holdings, and Rosemont Seneca Partners, along with a number of other contacts.

Grassley's office responded to Democrats' criticisms of the Treasury's compliance, saying, "it's unfortunate that Democrats whom we've kept in the loop on our investigations would recklessly seek to interfere with legitimate government oversight."