The Senate Judiciary Committee will vote on whether to release the transcripts of a closed hearing with the co-founder of the firm that commissioned the controversial dossier on President Trump.

"It will take a vote of the committee to do it, but I presume that they will be released," Judiciary Committee Chairman Chuck Grassley (R-Iowa) said at a Mount Ayr, Iowa, town hall meeting on Wednesday, The Washington Examiner reported.

Glenn Simpson, whose opposition research firm Fusion GPS commissioned the dossier, was questioned in a closed door hearing on Tuesday about the funding and sources behind the dossier.

The dossier, created by former British spy Christopher Steele, contained salacious information about connections between Trump and Russia, much of it unverified.

The president has denied the contents of the document.

Grassley said that the process of releasing Simpson's testimony would be lengthy, and Simpson and his lawyer would have to receive a copy of the testimony before it could be made public.

"It takes a long time for the court reporter to get it ready to go, but we'll have to give it to them before the thing you're asking me about can be done," the senator said, adding that he predicts the committee will vote to release the transcript.

"I don't know why I wouldn't. But I don't want to say so because I've never - in all the years I've been in Congress, well, I guess I've only been chairman of two committees, I've never gone through this process before. So I'm not going to answer your question until I get a firm footing of what the precedent is," he said.

Fusion GPS was originally used by Republicans to dig up opposition research on Trump during the party's 2016 primary. After the primary, the firm was paid by Democrats to continue the research.

Fox News reported the firm had handed over over 40,000 documents to the committee.

The committee is one of several congressional panels investigating Russian efforts to meddle in the presidential election and possible ties between the Trump campaign and the Kremlin.