Senate Judiciary Committee Chairman Chuck Grassley isn't backing down as the Justice Department rebuffs his repeated attempts to speak with the FBI agent whose interview with Michael Flynn was used to indict the ex-national security adviser in the Russia probe.

“This is no ordinary criminal case,” Grassley, R-Iowa, wrote in a June 6 letter to Deputy Attorney General Rod Rosenstein. “Congress has a right to know the full story and to know it now.”

Grassley is pressing his request anew after the DOJ once again rejected his bid to speak with FBI Agent Joe Pientka and to obtain the FBI’s records of the interview.

Flynn pleaded guilty in Special Counsel Robert Mueller’s Russia probe to making false statements to the FBI in that interview. He also lost his job at the White House after he was said to have misled Vice President Pence about a discussion with then-Russian ambassador Sergey Kislyak.

But Republicans on Capitol Hill are seeking more information about that interview as recent revelations have raised questions about the guilty plea itself. They say former FBI Director James Comey in fact indicated to lawmakers that FBI agents did not believe Flynn intentionally lied about the talks with Russia’s ambassador.

GRASSLEY PUSHES DOJ FOR ANSWERS ON FLYNN INTERVIEW

“Contrary to his public statements during his current book tour denying any memory of those comments, then-Director Comey led us to believe during that briefing that the agents who interviewed Flynn did not believe he intentionally lied about his conversation with the Ambassador and that the Justice Department was unlikely to prosecute him for false statements made in that interview,” Grassley wrote in May to Rosenstein and FBI Director Christopher Wray.

In that letter, Grassley requested the FBI’s so-called “302” documents memorializing their interview with Flynn and other supporting documents, including the agents’ notes. He also asked for a transcribed interview with Pientka, the FBI special agent who interviewed Flynn with fellow agent Peter Strzok, whose anti-Trump text messages later led to his dismissal from the Russia probe.

Assistant Attorney General Stephen Boyd, in a May 29 letter to Grassley, declined the requests.

“Whatever Mr. Corney may have said and whatever Mr. Flynn's demeanor, the evidence in the public record proves beyond any reasonable doubt that Mr. Flynn knowingly made false statements about contacts with the Russian ambassador,” Boyd said.

Boyd emphasized that Flynn “admitted under oath to making a materially false statement” and was represented by two experienced attorneys when he pleaded guilty to lying to FBI agents. He also expressed concern that handing over those documents or allowing an interview with a FBI agent would “unavoidably would create the appearance of political influence.”

“For this reason, the Department is obligated at this time to respectfully decline to provide documents or arrange for staffers to interview the agent named in your letter,” Boyd wrote.

Boyd also suggested an interview with Pientka is unnecessary because the DOJ is unaware of “any allegation against or previous publicity about the agent.”

Grassley, in his response to the Justice Department, took issue with that statement, calling it “disingenuous and extremely disturbing.”

“As you well know, seeking information from a fact witness is not the same thing as an allegation of wrongdoing,” Grassley said. “Quite the contrary, it seems he is likely to be an objective, reliable, and trustworthy witness, which is precisely why the Committee would benefit from his testimony.”

House Intelligence Committee Republicans' recently released Russia report also cited top FBI officials suggesting the agents who interviewed Flynn saw no indication Flynn knew he was lying.

The development is puzzling because Flynn’s comments were indeed at odds with the evidence. The FBI reportedly intercepted conversations that countered Flynn’s initial claim that, among other things, he did not ask Russia’s ambassador to refrain from escalating the situation in response to sanctions.

The request from Grassley comes as the Justice Department and other Republicans on the Capitol Hill have been sparring over access to documents concerning the FBI's alleged informant in contact with members of President Trump's 2016 campaign at the dawn of the Russia probe.

NUNES SETS DEADLINE FOR DOJ TO PROVIDE DOCUMENTS ON ALLEGED FBI INFORMANT

In a letter sent Friday to Rosenstein, House Intelligence Committee chairman Devin Nunes, R-Calif., said the records should be provided to all committee members "and designated staff" rather than just the so-called "Gang of Eight" -- which refers to Republican and Democratic leaders in both houses of Congress as well as top lawmakers from the intelligence panels.

"Your continued refusal to permit Members of Congress and designated staff to review the requested documents is obstruction of a lawful Congressional investigation," Nunes wrote.

Asked about the letter, however, a DOJ official said Rosenstein is currently “representing the United States in a brief unrelated visit to a foreign nation, one of America’s key intelligence partners,” indicating he would plan on responding during the previously scheduled briefing on Thursday.

“He, along with the FBI Director and DNI Coats, look forward to further briefing and again presenting responsive documents to Chairman Nunes and the rest of his colleagues in the Gang of 8 meeting scheduled for Thursday of this week,” the official said.

Fox News’ Pamela K. Browne, Catherine Herridge, Adam Shaw and Samuel Chamberlain contributed to this report.