Former FBI Deputy Director Andrew McCabe Andrew George McCabeGraham: Comey to testify about FBI's Russia probe, Mueller declined invitation Barr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' GOP votes to authorize subpoenas, depositions in Obama-era probe MORE is seeking legal immunity in exchange for his testimony on the agency's handling of the investigation into former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE's use of a private email server.

A lawyer for McCabe wrote to Senate Judiciary Committee Chairman Chuck Grassley Charles (Chuck) Ernest GrassleyThe Hill's 12:30 Report: Ginsburg lies in repose Top GOP senators say Hunter Biden's work 'cast a shadow' over Obama Ukraine policy Read: Senate GOP's controversial Biden report MORE (R-Iowa) on Tuesday seeking a guarantee of immunity for McCabe's testimony before the panel, writing that the former FBI official would plead the Fifth if prompted to testify otherwise, CNN reported.

"Mr. McCabe is willing to testify, but because of the criminal referral, he must be afforded suitable legal protection," McCabe attorney Michael Bromwich wrote to Grassley, according to CNN.

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"This is a textbook case for granting use immunity ... If this Committee is unwilling or unable to obtain such an order, then Mr. McCabe will have to no choice but to invoke his Fifth Amendment privilege against self-incrimination."

McCabe is the subject of a criminal referral from the agency's inspector general, which has reportedly found that McCabe acted inappropriately by leaking information to a reporter and then lying about it to then-FBI Director James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE.

Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE fired McCabe in March, citing the internal review that found McCabe "lacked candor." McCabe has insisted he acted within his authority in authorizing FBI officials to talk to a reporter about an ongoing investigation surrounding the Clinton Foundation in 2016.

Grassley has also invited Comey, as well as former Attorney General Loretta Lynch, to testify before the committee about the Clinton email investigation, sources told CNN.

President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE has repeatedly and publicly attacked McCabe over donations to his wife's unsuccessful state Senate campaign in Virginia in 2015 from a group led by then-Virginia Gov. Terry McAuliffe (D), a close Clinton family ally.

The president has called for an investigation into McCabe, whom he blames for bringing the investigation into Clinton to an end.

In April, Bromwich announced that McCabe planned to retaliate by suing Trump for defamation, and was considering other charges.