The U.S. Treasury Department has started turning over confidential banking records related to Hunter Biden in response to requests from Senate investigative committees.

Senate Finance Committee Chairman Chuck Grassley and Senate Homeland Security and Governmental Affairs Committee Chairman Ron Johnson asked the Treasury in November for "suspicious activity reports," banking alerts involving money laundering or fraud, related to Biden and his associates.

A spokeswoman for Sen. Ron Wyden, the ranking Democrat on the Senate Finance Committee, told Yahoo News that the department has already started turning over records. The Wyden spokeswoman criticized the Treasury Department for "rapidly complying" with the requests, calling the Republican-led Senate investigation of Biden a "sideshow.”

“Applying a blatant double standard, Trump administration agencies like the Treasury Department are rapidly complying with Senate Republican requests — no subpoenas necessary — and producing ‘evidence’ of questionable origin,” said Wyden spokeswoman Ashley Schapitl.

A spokesman for Grassley said he could not elaborate on what the records contained at this time but criticized Democrats for "recklessly" seeking to interfere with the investigation.

"As a matter of routine, we don’t discuss sensitive third-party material during ongoing investigations. It’s unfortunate that Democrats whom we’ve kept in the loop on our investigations would recklessly seek to interfere with legitimate government oversight," Grassley's spokesman, Taylor Foy, told the Washington Examiner.

Grassley's and Johnson's committees have been investigating whether the Obama administration took official action to help the business interests of Biden while his father, Joe Biden, was vice president. The Republican senators asked the Treasury's Financial Crimes Enforcement Network for suspicious activity reports involving Hunter Biden, his business partner Devon Archer, their firm, Rosemont Seneca Partners, the Ukrainian oil company Burisma Holdings, and other related companies and individuals. In the letter, they asked the department to turn over the records by Dec. 5, 2019.

Banks and financial institutions are required to file "suspicious activity reports" when they notice unusual transactions that could indicate illegal activities such as money laundering, financing of terrorism, or fraud.

A spokesperson for Johnson did not respond to a request for comment. On Wednesday, Grassley and Johnson also requested Hunter Biden's official travel records from the U.S. Secret Service.

[Read more: Hunter Biden renting $12,000-per-month Hollywood home while refusing to pay child support]