Senate Judiciary Committee Chairman Lindsey Graham (R-S.C.) asked special counsel Robert Mueller if he wanted to dispute part of Attorney General William Barr’s testimony regarding a phone call the two had about Mueller’s report, adding to tension between the Justice Department and the special counsel.

Graham offered the suggestion to Mueller in a letter Friday, specifically asking for the special counsel’s opinion on the call, which Barr had described in testimony before the Judiciary Committee on Wednesday.

During that hearing, Barr said Mueller told him that he thought the press surrounding the probe into Russia’s meddling in the 2016 election was misleading. Barr also described Mueller’s response to the attorney general’s four-page summary of the special counsel’s findings released in late March. Barr claimed Mueller said he did not find the summary inaccurate.

Graham’s letter did not explicitly request Mueller’s appearance. Instead, the senator suggested Mueller respond to Barr’s testimony, which would further drag Mueller into rising tensions between the special counsel and Republicans.

“Please inform the Committee if you would like to provide testimony regarding any misrepresentation by the Attorney General of the substance of that phone call,” Graham wrote to Mueller.

Graham also noted that Barr said Mueller wanted more details of the report released publicly, specifically their summaries on whether the president obstructed justice.

On March 27, weeks before Barr’s Senate hearing, Mueller sent a letter to the Justice Department complaining that the attorney general’s summary “did not fully capture the context, nature, and substance” of the special counsel report.

Mueller accused Barr of causing “public confusion about critical aspects of the results of our investigation.”

“This threatens to undermine a central purpose for which the Department appointed the Special Counsel: to assure full public confidence in the outcome of the investigations,” Mueller told Barr.

In light of Mueller’s letter, which was first reported by The Washington Post on Tuesday, Democrats called on Barr to resign.

Rep. Adam Schiff (D-Calif.) decried what he called Barr’s “deliberately false and misleading” testimony to a House panel last month, in which Barr said he didn’t know of any concerns Mueller had about his summary of the special counsel’s report.

“If he were an ordinary citizen, it might be considered perjury. As our top law enforcement official, it’s even worse,” Schiff tweeted. “He must step down.”