Senate Judiciary Committee Chairman Chuck Grassley's office told the founders of Fusion GPS on Wednesday that if they want the world to know what they told him in a closed session about their role in creating the Trump dossier, they should testify in public.

Grassley's staff issued that challenge to Fusion GPS after the company's co-founders, Glenn Simpson and Peter Fritsch, argued in a New York Times op-ed that Grassley should release the testimony they delivered to his committee privately in August.

"Republicans have refused to release full transcripts of our firm’s testimony, even as they selectively leak details to media outlets on the far right. It’s time to share what our company told investigators,” the pair wrote in the op-ed.

The two testified about Fusion GPS's role in creating the dossier, which was written by former British intelligence officer Christopher Steele and contained salacious allegations linking President Trump to Russia. Trump supporters say the dossier triggered the numerous investigations into Russian meddling in the 2016 election and possible collusion with the president’s campaign.

Grassley spokesman Taylor Foy said Simpson only agreed to testify in that closed setting, and said Grassley "has always been and remains for transparency.”

“There are, however, investigative factors that [Grassley] must consider to temporarily protect certain information in the midst of an ongoing inquiry such as this one, like tainting the memory of other witnesses," Foy said. "More importantly, Senator Grassley provided Fusion GPS an opportunity for transparency six months ago when he invited the firm to publicly testify at an open committee hearing. Mr. Simpson declined."

Foy added that Simpson has “refused to answer dozens of questions voluntarily, and has failed to provide the committee with documents and responses to follow-up questions after the interview.”

Thus, “the committee’s invitation for Mr. Simpson to testify at a public hearing remains on the table," Foy said.