The co-founder of Fusion GPS, the opposition research firm that produced the now-infamous Trump-Russia dossier, will invoke his First and Fifth Amendment privileges in order to avoid testifying before the House Judiciary Committee next week, his lawyer said Thursday.

The committee had subpoenaed Glenn Simpson to appear for a closed-door deposition last month after attorney Joshua Levy said his client would not participate voluntarily. Simpson has previously sat for three congressional interviews as part of investigations into Russian activities during the 2016 presidential election campaign.

In a letter to committee chairman Bob Goodlatte, R-Va.,  Levy accused Republicans on the panel of trying to “discredit and otherwise damage witnesses to Russia’s interference in the 2016 election, all as part of an effort to protect” President Trump. Levy added that the committee “has abdicated and indeed perverted its constitutional and traditional role” and shown “abundant bad faith” toward Simpson.

GOP lawmakers have focused on the relationship between Simpson and Justice Department official Bruce Ohr, who was also in contact with former British spy Christopher Steele. Fusion GPS commissioned Steele to compile his research on Trump’s alleged personal and financial ties to Russia into a dossier. The dossier became part of the evidence used to obtain a secret surveillance warrant to monitor former Trump campaign adviser Carter Page and was published by BuzzFeed News in January 2017.

In previous testimony, Simpson told lawmakers on the Senate Intelligence Committee that he did not have contact with Ohr until after the 2016 election. However, work emails written by Ohr show the two were in touch that August, if not earlier. Ohr’s notes also indicate that in December 2016, there was a meeting in Washington, D.C.’s Chinatown between Fusion GPS’ Simpson and Ohr, with Ohr writing, “Glen(n) gave me a memory stick.”

In addition, Ohr maintained extensive contact with Steele for months after the bureau cut ties with the former MI6 man in November 2016 for leaking information to the media about his FBI ties.

Fox News’ Catherine Herridge and The Associated Press contributed to this report.