The Treasury Department complied with a Republican-controlled Senate inquiry into Hunter Biden's business dealings in Ukraine and handed over highly sensitive financial records and "evidence of questionable origin," a report on Thursday said.

Biden, the son of former Vice President Joe Biden, has been a favorite target for President Trump and other Republicans who use him as an example of an extreme case of crony capitalism. He once held a $50,000-a-month job with Ukrainian gas giant, Burisima Holdings while his father served under then-President Obama. His father was tasked with handling Ukraine policy at the time.

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Joe Biden, who is running for president, has consistently said his son did nothing wrong.

Yahoo News first reported that the Treasury Department began to turn over the documents related to the Senate inquiry late last year.

Sens. Charles Grassley, R-Iowa, the chairman of the Senate Finance Committee, and Ron. Johnson, R-Wisc., the chairman of the Homeland Security and Governmental Affairs Committee, requested the records in the form of a suspicious activity report, also known as a SARs. They also requested financial records through FinCEN, which is a branch of the Treasury Department that eyes money laundering.

Sen. Ron Wyden, D-Ore., who sits on the Finance Committee, told Yahoo News that the swift response from Treasury is a "blatant double standard" considering how the Trump administration responded to Democrats' effort to obtain documents and witness testimony in his impeachment trial.

"The administration told House Democrats to go pound sand when their oversight authority was mandatory while voluntarily cooperating with the Senate Republicans’ sideshow at lightning speed," a spokesman from Wyden told the website.

Grassley refused to identify what information Treasury provided when reached by The New York Times, but said through a spokesman, "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 and Johnson announced in a letter Wednesday they are also seeking “records of Hunter Biden’s travel while he was under U.S. Secret Service protection as they continue to investigate potential conflicts of interest to boost his business ventures in Ukraine and China."

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"We write to request information about whether Hunter Biden used government-sponsored travel to help conduct private business, to include his work for Rosemont Seneca and related entities in China and Ukraine," the senators wrote, referring to the company co-founded by the younger Biden.

Trump's impeachment trial was based on a phone call he had with his Ukrainian counterpart in which he asked him to investigate the Bidens' dealings in the country. Democrats alleged that Trump withheld military funding in order to put pressure on Kiev. Trump denied any wrongdoing, was impeached in the House and acquitted in the Senate impeachment trial.

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The Treasury Department did not immediately respond to an after-hours email from Fox News.

Fox News' Gregg Re contributed to this report