Executives with Fusion GPS — producers of the Trump dossier — pleaded the fifth in testimony to the House intelligence committee Wednesday morning, according to a source familiar with the matter.

Fusion GPS executives Peter Fritsch and Thomas Catan pleaded the fifth to every single question asked during the roughly half an hour session, the source said, including to basic questions such as “Who funded the dossier?”

“They both plead the fifth to every question that was put to them,” the source said.

The committee interviewed them as part of its ongoing investigation into Russia’s meddling in the 2016 election and any potential collusion with the Trump administration. Rep. Michael Conaway (R-TX), who is leading the investigation, issued the subpoenas for Fusion GPS representatives to come in, according to another source familiar with the subpoenas.

The firm’s co-founder, former Wall Street Journal reporter Glenn Simpson, is set to testify to the committee in upcoming weeks.

The dossier made unfounded and salacious claims about Trump that have been unverified and considered unreliable. Fusion GPS hired ex-British spy Christopher Steele to create the dossier, but it’s unknown who his sources were.

The dossier was reportedly used by the FBI to obtain a FISA surveillance warrant on members of the Trump campaign and launch the FBI investigation against the Trump campaign. So far there has been no evidence that the Trump campaign colluded with Russia on the election.

The dossier was reportedly funded by Republicans who were against Trump, and then after the primary, funded by Hillary Clinton supporters. The FBI also reportedly considered funding the firm to continue work on the dossier, but it’s not known whether there were any payments made.

“We’ve been trying very hard to get information about the Steele dossier,” the source said. “The particular question that we wanted to know from Fusion GPS was ‘Who funded it?’ And also just basic information about how it was put together and how it was verified.”

The committee has been trying to get information from the FBI and the Department of Justice about their history with the dossier — how they got it, whether they used it as justifications for FISA warrants, the source said.

“We’ve been completely stonewalled for months, and this has been an ongoing thing,” the source said.

“So you have what seems to be the Democrats, and Fusion GPS and these officials — intelligence agency bureaucrats — all blocking every single attempt we’re making to get the most basic information about this document, which … may have been the single document that sparked the entire Russia investigation in the first place.”

Democrats on the intelligence committee have slammed efforts to learn more about the dossier, calling it a “distraction” from whether the Trump campaign colluded with Russia.

“Anything that distracts from that is useless for them,” the source said.