Three key figures connected to the infamous, Democrat-funded anti-Trump dossier have been called to testify on Capitol Hill this week, as the House investigation into Justice Department actions during the 2016 campaign comes to a head.

However, Glenn Simpson, the co-founder of the Fusion GPS research group that commissioned the dossier, will invoke the Fifth Amendment right not to testify when he appears before the House Judiciary Committee on Tuesday, his lawyer, Joshua Levy, announced late Monday.

"Compelling Glenn Simpson to appear for a confidential deposition after he has stated his intention to invoke his constitutional right not to testify reflects the worst practices of past congressional investigations and reinforces that this is a political exercise, not a serious inquiry," Levy wrote in a statement.

A deposition is also scheduled for Thursday with James A. Baker, the FBI’s former top lawyer. Baker, who had a close working relationship with former FBI Director James Comey, left the bureau earlier this year.

The dossier, authored by former British spy Christopher Steele and commissioned by Fusion GPS, was paid for by the Democratic National Committee and Hillary Clinton's presidential campaign through law firm Perkins Coie. It included salacious and unverified allegations about Trump's visit to Russia.

Earlier this month, Baker testified about the genesis of the bureau’s Russia investigation, sources close to a congressional investigation told Fox News. He also testified that Perkins Coie lawyer Michael Sussmann gave him documents pertaining to the Russia probe, suggesting another connection between the early stages of the FBI’s Russia probe and those working with the DNC and the Clinton campaign, the sources said.

House Republicans have also scheduled a deposition for Friday with Nellie Ohr, a Russia researcher for Simpson’s company. Ohr is married to Bruce Ohr, a Justice Department official who has also testified about his contact with Simpson during the campaign.

Baker and Ohr are appearing for voluntary depositions, which take place as transcribed interviews under oath.

The dossier, which has been at the center of an intense power struggle between congressional Republicans and the FBI, specifically cites the DOJ and FBI’s surveillance of Trump campaign adviser Carter Page, saying the dossier "formed an essential part" of the application to spy on him.

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Fox News learned Monday that Page has filed suit in Oklahoma against the DNC, as well as the law firm Perkins Coie, and its principals Marc Elias and Sussman over the dossier, and what Page claims were “slanderous” and “libelous” statements.

"It goes beyond any damages or any financial aspect," Page told Fox News' "Hannity" Monday night. "There have been so many lies. You look at the damage it did to our democratic systems and our institutions of government back in 2016, and I'm just trying to get some justice in terms of getting some disclosure."

Meanwhile, Virginia GOP Rep. Bob Goodlatte, the chairman of the House Judiciary Committee, is considering a subpoena for Deputy Attorney General Rod Rosenstein, who oversees Special Counsel Robert Mueller’s Russia investigation.

"It's essential that we talk to him. He knows that. He has not agreed to come for a transcribed interview on the record. He needs to agree to do that. If he does not agree to do that very soon, I will issue a subpoena for him to appear," Goodlatte said Saturday during a Fox News appearance.

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House Republicans had called for Rosenstein to testify last week about reports the Justice Department official suggested secretly wearing a wire to record the president. But talks over the details of that testimony reached an impasse.

The New York Times first reported the details of the alleged discussions between Rosenstein and senior FBI officials in May 2017, one day before Rosenstein appointed Special Counsel Robert Mueller to oversee the Russia investigation.

After the allegations surfaced last month, Rosenstein released a statement saying: "I never pursued or authorized recording the President and any suggestion that I have ever advocated for the removal of the President is absolutely false."

Fox News’ Chad Pergram and Cyd Upson contributed to this report.