A top prosecutor on the team investigating Hunter Biden is facing scrutiny amid allegations she limited questioning and inquiries about President Biden and blocked search warrants because she was worried about "optics" during the years-long probe.

Pressure is building on Assistant U.S. Attorney Lesley Wolf following the release of whistleblower testimony from IRS officials involved in the probe into Hunter Biden who say the investigation was improperly influenced by politics.

One whistleblower, Gary Shapley Jr., who was the supervisor of the investigation at the IRS, said that "at every stage" of the Hunter Biden probe, decisions were made that "had the effect of benefiting" the president’s son.

Shapley made a number of damning allegations that cast doubt over the legitimacy of the years-long investigation, and lobbed critical accusations at Wolf.

HOUSE GOP DEMAND TRANSCRIBED INTERVIEWS FROM HUNTER BIDEN PROSECUTOR, DOJ, IRS, SECRET SERVICE OFFICIALS

The Department of Justice (DOJ) building

The Department of Justice denied allegations of political interference in the Hunter Biden investigation. (Kent Nishimura / Los Angeles Times via Getty Images)

According to Shapley, Wolf worked to "limit" questioning related to President Biden and apparent references to Biden as "dad" or "the big guy."

Wolf allegedly said there was "no specific criminality to that line of questioning" relating to President Biden, which Shapley said "upset the FBI."

In October 2020, Wolf reviewed an affidavit for a search warrant of Hunter Biden’s residence, and "agreed that probable cause had been achieved," Shapley testified. However, Shapley said Wolf ultimately would not allow a physical search warrant on the president’s son.

Shapley said Wolf determined there was "enough probable cause for the physical search warrant there, but the question was whether the juice was worth the squeeze."

HUNTER BIDEN INVESTIGATORS LIMITED QUESTIONS ABOUT 'DAD,' 'BIG GUY' DESPITE FBI, IRS OBJECTIONS: WHISTLEBLOWER

Hunter Biden, son of Joe Biden

Hunter Biden arrives at Fort Lesley J. McNair in Washington, D.C., on Tuesday, July 4, 2023. (Ting Shen/Bloomberg via Getty Images)

Wolf allegedly said that "optics were a driving factor in the decision on whether to execute a search warrant," Shapley said, adding that Wolf agreed that "a lot of evidence in our investigation would be found in the guest house of former Vice President Biden, but said there is no way we will get that approved."

Wolf also allegedly tipped off Hunter Biden’s legal team ahead of a planned search of his storage unit.

In light of these allegations, top congressional lawmakers are demanding answers from the Justice Department on Wolf’s prosecutorial decisions.

The Justice Department has denied that decisions made in the Hunter Biden investigation were influenced by politics.

DOJ BRIEFED HUNTER BIDEN TEAM ON JOE BIDEN ALLEGATIONS, BUT EXCLUDED IRS AGENTS: GRASSLEY

Hunter Biden gets off plane with president

President Biden, left, has snapped at reporters who have asked him about alleged corruption involving him and his son, Hunter Biden. (AP Photo/Patrick Semansky)

The House Judiciary Committee has asked Wolf to appear before the panel for a transcribed interview as part of its oversight investigation into the DOJ’s handling of the Hunter Biden probe. That committee has also called on U.S. attorney for Delaware David Weiss, who is leading the Hunter Biden investigation, for a transcribed interview.

It is unclear if Wolf will sit for the transcribed interview.

In the Senate, Sen. Chuck Grassley, R-Iowa, revealed that Wolf was briefed on a key FBI document containing allegations of a criminal bribery scheme involving then-Vice President Joe Biden.

The document in question is an FBI-generated FD-1023 form. The form, dated June 30, 2020, reflects the FBI's interview with a "highly credible" confidential source who detailed multiple meetings and conversations he or she had with a top executive of Ukrainian natural gas firm Burisma Holdings over the course of several years, starting in 2015.

EXCLUSIVE: JOE BIDEN ALLEGEDLY PAID $5M BY BURISMA EXECUTIVE AS PART OF A BRIBERY SCHEME, ACCORDING TO FBI DOCUMENT

Hunter Biden sat on the board of Burisma, and the executive alleged a $5 million payment was made to Hunter and $5 million to Joe Biden in exchange for influence over policy decisions.

IRS agent Gary Shapley sits down on the Fox News Channel "Special Report" set for an interview

IRS Criminal Supervisory Special Agent Gary Shapley Jr., defended his claims that the Justice Department interfered with U.S. Attorney David Weiss' Hunter Biden investigation in an interview with Fox News' "Special Report." (Fox News)

Grassley is now demanding answers was to whether Wolf obstructed any investigative steps surrounding the FD-1023 form, in light of her alleged actions to block questioning related to President Biden throughout the investigation.

The Justice Department last month announced that the president’s son had entered a plea agreement that will likely keep him out of jail. Hunter Biden is set to plead guilty to two misdemeanor counts of willful failure to pay federal income tax, and to one charge of possession of a firearm by a person who is an unlawful user of or addicted to a controlled substance.

CLICK HERE TO GET THE FOX NEWS APP

Hunter Biden is expected to make his first court appearance on July 26.

The federal investigation into Hunter Biden began in 2018.