The feud between Sen. Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans signal openness to working with Biden Senators offer disaster tax relief bill Trump spikes political football with return of Big Ten season MORE (R-Iowa) and Fusion GPS just keeps getting more heated.

Joshua Levy, a lawyer for the opposition research firm, fired back at the Judiciary Committee chairman on Wednesday after Grassley accused Fusion GPS co-founder Glenn Simpson of declining to testify publicly about his firm's controversial dossier linking President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE to Russia.

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Levy in a statement said his client had already testified for 10 hours and that Grassley should release that transcript, something Simpson and co-founder Peter Fritsch previously argued in an op-ed in The New York Times on Tuesday.

"Should the Committee choose to release his testimony, the public will see a 300-page transcript covering 10 hours of questions and answers," Levy wrote in a statement.

The lawyer also criticized Grassley for not pressing for former Trump campaign chairman Paul Manafort Paul John ManafortBannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention Ukraine language in GOP platform underscores Trump tensions MORE or Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE, to testify before his panel, and for not subpoenaing other members of Trump's campaign, arguing the chairman is not actually interested in getting to the truth of Russia's involvement in the 2016 election.

“We appreciate the Chairman’s interest in Fusion’s appearance at a hearing,” Levy wrote. “But why hasn’t he pressed Mr. Manafort to testify? Why hasn’t he asked Mr. Trump, Jr. to come back and answer further questions? Why hasn’t he served a subpoena on other members of the Trump campaign? What about Russian oligarchs with ties to Putin, individuals who travel freely in this country?"

“The Committee has long known that Fusion GPS is neither the story nor the reason why the U.S. government is investigating the president’s campaign,” he added. “We suggest Chairman Grassley acknowledge that fact and be transparent with the American people.”

The war of words began Tuesday with the blistering op-ed from Simpson and Fritsch, which Grassley responded to on Wednesday in a statement criticizing Simpson for declining to testify publicly.

"Senator Grassley provided Fusion GPS an opportunity for transparency six months ago when he invited the firm to publicly testify at an open committee hearing. Mr. Simpson declined. When faced with a subpoena from the Chairman and Ranking Member, Mr. Simpson refused to provide public testimony, using his Fifth Amendment right against self-incrimination to negotiate for a closed-door interview," Grassley's office said in a Wednesday statement.

"Despite his public statements, Mr. Simpson and his attorney demanded during the interview that the transcript be kept confidential. Mr. Simpson has refused to answer dozens of questions voluntarily, and has failed to provide the Committee with documents and responses to follow-up questions after the interview," it continued.

Levy said his client has previously said that the committee should release the testimony of his transcript. Fusion GPS's founders said Republicans have been selectively leaking information from Simpson's testimony.

“The Chairman has the authority to call a vote of the Committee to release Mr. Simpson’s transcript,” Levy said in his statement Wednesday afternoon. “He should do so."

“We have consistently supported release of the transcript, so long as we would have the opportunity to review it for accuracy, and so long as the identities of Fusion’s bank and employees could be protected,” Levy said. “Fusion GPS has received numerous threats in the past year.”