Senate Intelligence Committee Chairman Richard Burr on Wednesday threatened to subpoena the authors of a "dossier" that was published days before Trump's inauguration that raised questions about Trump's ties to Russia.

"I strongly suggest that you come in and speak with us," Burr said to authors of the dossier. "If we believe that you have something valuable to bring to the committee, if you don't voluntarily do it, I will assure you today, you will be compelled to do it. I can compel you to come, I can't compel you to talk. But that will be in a very — done in a very public way if, in fact, you turn down the private offer."

Fusion GPS was the company that paid Christoper Steele to create the dossier. The document has been of particular interest to Republicans because the document is believed to have been an opposition research document built during the campaign that included potentially damaging information against Trump.

There is dispute over whether the dossier was first begun by Republicans who wanted to hurt Trump before he won the Republican primary, but it is widely believed at some point the dossier was taken over by opponents to Trump outside just his Republican adversaries.

Burr said his committee has "hit a wall" on investigating the dossier, and said it has had no luck so far getting Steele to testify.

"We have on several occasions made attempts to contact Mr. Steele to meet with Mr. Steele, to include personally the vice chairman and myself as two individuals making that connection," Burr said.

"Those offers have gone unaccepted," he added. "The committee cannot really decide the credibility of the dossier without understanding things like, who paid for it? Who were your sources and subsources? We're investigating a very expansive Russian network of interference in U.S. elections. And though we have been incredibly enlightened at our ability to rebuild backwards the Steele dossier up to a certain date, getting past that point has been somewhat impossible."

Previous media reports said the FBI may have paid or offered to pay Fusion GPS to continue its work with Steele on assembling the dossier, and another media report has said the dossier was used to obtain a warrant to surveil Carter Page, who briefly served in the Trump campaign in 2016.