Paul Manafort. Drew Angerer/Getty Images Attorneys for President Donald Trump's campaign chairman, Paul Manafort, are reportedly blocking Robert Mueller, the special counsel leading the FBI's Russia investigation, from obtaining a transcript of his interview with the Senate Intelligence Committee in July.

CNN reported on Tuesday that a dispute had erupted between the FBI, which said it had obtained authorization from Manafort's attorneys to view the transcript, and the committee, which says it was instructed by the attorneys not to hand it over.

Mueller's team has apparently gotten permission to view the documents Manafort submitted to the committee about the meeting he attended last June at Trump Tower with two Russian lobbyists and Donald Trump Jr., the president's eldest son. Trump's son-in-law, Jared Kushner, was also present.

But the committee hasn't turned over those documents yet, either, according to CNN. Manafort's spokesman did not return phone calls requesting comment.

Renato Mariotti, a federal prosecutor turned defense attorney, explained on Tuesday that Manafort's attorneys were most likely arguing that they agreed with Mueller before Manafort appeared before the committee — which does not have prosecution power — that his testimony would not be used against him by the FBI in its criminal investigation.

In that sense, they may be arguing a form of quasi-immunity. But unless Manafort got that in writing, it is unlikely to hold up in court, Mariotti said in an interview. And while Congress may be waiting for the Mueller-Manafort spat to blow over, it is ultimately not obligated to keep the transcript private.

Manafort's attorneys' reluctance to allow Mueller to view the transcript, moreover, is likely to raise red flags for the FBI and prompt it to take more aggressive measures to obtain it.

Manafort has emerged as a focal point of the FBI probe, which recently recruited New York Attorney General Eric Schneiderman to help investigate the longtime political operative for possible financial crimes and money laundering. The IRS's criminal-investigations unit has been brought onto the investigation to examine similar issues, according to The Daily Beast, though it is unclear to what extent its work will focus on Manafort.

Mueller's team obtained a search warrant to raid Manafort's home in July. Sources told CNN that investigators might have taken documents protected by attorney-client privilege, but Mariotti said on Twitter that "incriminating" evidence "in plain view" and spotted by FBI agents during a raid was fair game.

Obtaining a warrant after the fact to put into evidence documents not covered under the scope of the initial warrant is also common, Mariotti said.

If any of those documents contradict what Manafort told the Senate Intelligence Committee, Mueller could use that as evidence of perjury. He could also use the congressional testimony as a point of comparison if he subpoenaed Manafort to appear before a grand jury — assuming, that is, that Manafort wouldn't invoke his Fifth Amendment right against self-incrimination.

Manafort's presence at the Trump Tower meeting came under intense scrutiny last week when NBC reported that he had been taking notes on his iPhone that referenced political contributions and the Republican National Committee.

Congressional investigators examining Russia's interference in the 2016 presidential election are now using Manafort's notes as a jumping-off point to examine whether the Trump campaign or the RNC received donations from Russian sources after the meeting, according to NBC.

Democratic Rep. Eric Swalwell, a member of the House Intelligence Committee, told Business Insider on Tuesday that the committee "must" interview Manafort.

"Manafort is a critical witness," Swalwell said. "He was chairman at a time direct communications occurred between the Trump campaign and Russia."

Swalwell said last week that "a complete investigation will answer whether the Russians were working with the Trump campaign and whether that included financial assistance."

"There are enough accounts out there that we should probe further to see if that was the case," he added, pointing to the meeting and the recent revelations about the Trump Organization pursuing a real-estate deal in Moscow during the election.

"Clearly, we have to keep following the money."