The Treasury Department has promoted two IRS whistleblowers who accused the Justice Department under President Joe Biden of granting his son, Hunter Biden, special treatment during a yearslong probe into his tax affairs.

Gary Shapley and Joseph Ziegler, two veteran IRS investigators, will serve as senior advisors to incoming Treasury Secretary Scott Bessent, who said in a statement on Tuesday that he was “pleased to welcome Gary Shapley and Joseph Ziegler to the Treasury Department, where they will help us drive much-needed cultural reform within the IRS.”

Shapley and Ziegler came forward in 2023 with allegations that the Biden administration improperly interfered in an investigation into Hunter Biden’s unpaid taxes led by then-U.S. Attorney for Delaware David Weiss — claims that Justice Department and FBI officials fiercely disputed at the time.

“It appeared to me, based on what I experienced, that the U.S. Attorney in Delaware in our investigation was constantly hamstrung, limited and marginalized by DOJ officials,” Ziegler said during congressional testimony in July 2023.

Days after Shapley and Ziegler testified on Capitol Hill, a plea deal negotiated by Hunter Biden and the Justice Department fell apart under questioning from a federal judge. The deal would have allowed Hunter Biden to plead guilty to a pair of tax-related misdemeanors and enter into a pretrial diversion agreement on a felony gun charge.

Weiss, the Trump-appointed prosecutor who led the probe into Hunter Biden, repeatedly refuted the claims leveled by Shapley and Ziegler and asserted that he faced no political pressure from Biden administration officials to grant Hunter Biden any special treatment.

Hunter Biden later pleaded guilty to nine tax-related charges, including multiple felonies. His father granted him a sweeping pardon in the waning weeks of his presidency.

Sen. Chuck Grassley, R-Iowa, touted his role in securing promotions for Shapley and Ziegler in a statement Tuesday. Grassley said he wrote Bessent multiple letters encouraging him to promote the two whistleblowers, and that “today’s announcement is a result of Grassley’s direct request.”

“Gary Shapley and Joe Ziegler put their entire careers on the line to stand up for the truth, and instead of being thanked, the Biden administration treated them like skunks at a picnic,” Grassley wrote in a press release. “I hope today is the first of many redemption stories for whistleblowers who’ve been mistreated.”

Shapley will serve as Deputy Chief of IRS Criminal Investigations and Ziegler will be assigned to the secretary’s office as a senior adviser for IRS reform.