The co-founder of the opposition research firm that hired former British spy Christopher Steele to assemble a dossier portraying links between President Trump and Russia has refused an invitation to interview before the House Judiciary and House Oversight committees.

The lawyers for Glenn Simpson said the Republican-led committee's “task force” and its investigation into Justice Department and FBI actions ahead of the 2016 presidential election “has demonstrated a propensity to flout rules of confidentiality in order to manipulate the record and prejudice witnesses.”

“The ‘task force’ smears of whistleblowers and responsible government actors have continued from antecedent practices of the President’s allies on the Hill,” wrote the lawyers .

Simpson’s firm Fusion GPS hired Steele after being financed but the Democratic Party to conduct the opposition research and compile the dossier.

The dossier was then used in part to obtain a surveillance warrant on Trump campaign aide Carter Page, but Republicans have said the political motivations behind the dossier were not fully revealed when applying for and obtaining the warrant.

Because of that, the FBI’s greater investigation into Russian election interference and the Trump campaign is biased, Republicans say.

GOP lawmakers on the two committees announced last fall that they would be looking into the FBI and Justice Department’s actions during the 2016 election.

In a six-page letter rejecting the invitation to appear before the House Judiciary and Oversight committees, Levy noted that Simpson has already given more than 20 hours of testimony to the Senate Intelligence Committee, the Senate Judiciary Committee, and the House Intelligence Committee.

"The so-called 'task force,' formed by members of the two committees you chair, has demonstrated a propensity to flout rules of confidentiality in order to manipulate the record and prejudice witnesses," the lawyers said. “Much of Mr. Simpson’s information, including testimony that was harshly ridiculed by Republican members, has now been substantiated.”

The letter was addressed to both Goodlatte and House Oversight Committee Chairman Trey Gowdy, R-S.C.