Republicans have demanded information about a discredited FBI informant whose claims formed the basis of their probe into President Joe Biden.
Alexander Smirnov was charged with giving false statements to agents last month after 14 years as an FBI source.
He fabricated claims that a Ukrainian energy firm paid bribes to Hunter Biden and his father, prosecutors said.
The lawmakers claimed that the charges raised concerns about the FBI’s vetting of confidential sources.
In a letter to FBI Director Christopher Wray, Republican congressmen Jim Jordan and James Comer, the chairs of the House Judiciary and Oversight committees, asked for documents showing how federal agents vetted the informant and how much they paid him.
Mr Smirnov’s testimony was a key part of their ongoing impeachment investigation launched last year.
“Only after Mr Smirnov reported that President Joe Biden accepted a bribe from a Ukrainian energy company in exchange for using his official position to oust the Ukrainian Prosecutor General did the FBI apparently take a hard look at this CHS [confidential human resource],” the lawmakers wrote.
“During the intervening period, the FBI represented to Congress that the CHS was ‘highly credible’ and that the release of his information would endanger Americans.”
The two lawmakers gave the FBI until 15 March to provide documents concerning any FBI wrongdoing or inaccurate reporting on Mr Smirnov.
Mr Jordan and Mr Comer, who are leading the impeachment inquiry into President Joe Biden, also asked for documents relating to an FBI probe into the bribery allegations involving Mr Biden.
Prosecutors allege that Mr Smirnov, 43, falsely claimed that an executive at Ukrainian energy company Burisma told him in 2015 or 2016 that the company paid the Bidens as much as $5m (£3.9m) in bribes each.
The FBI initially rejected lawmakers’ requests to turn over documents related to the claim, arguing it would reveal their confidential source.
Eventually, some lawmakers were allowed to review the record, which they used as central evidence in their impeachment trial against Mr Biden.
Mr Smirnov was indicted in February on charges of making a false statement and creating a fictitious record, with prosecutors alleging he did not meet the Burisma executive until years after he had claimed.
He has pleaded not guilty and is awaiting trial in jail. Prosecutors asked that Mr Smirnov be held without bail, citing alleged “extensive” contacts with Russian intelligence agencies.
Mr Comer and Mr Jordan claimed his arrest “raises even greater concerns about abuse and mismanagement in the FBI’s” confidential source programme.
The letter comes after Republicans released a transcript of testimony from Hunter Biden before the House Oversight Committee. The party has accused President Biden of being improperly involved in his son’s foreign business dealings.
The 229 pages of testimony offered few new insights. Hunter Biden focused on defending his father.
“For more than a year, your committees have hunted me in your partisan political pursuit of my dad,” he said in opening statements.
“You have trafficked in innuendo, distortion, and sensationalism, all the while ignoring the clear and convincing evidence staring you in the face: You do not have evidence to support the baseless and MAGA-motivated conspiracies about my father because there isn’t any.”
