Congressional Democrats are struggling to protect the identity of the U.S. government official who filed a whistleblower complaint about President Donald Trump’s Ukraine policy. And those efforts have fueled friction behind closed doors.

House Intelligence Committee Chairman Adam Schiff (D-CA) ruled in a closed-door deposition Tuesday morning that any questions that might lead to the revelation of the whistleblower’s identity were out of order, according to two sources familiar with the meeting.

His move frustrated Republicans. One source relayed that Rep. Eric Swalwell (D-CA) and Rep. Mark Meadows (R-N.C.) ended up “yelling at each other” during a closed door deposition of Alexander Vindman, the National Security Council Director for European Affairs who testified that he raised internal concerns about Trump’s call with Ukrainian President Volodymyr Zelensky that is now at the center of the impeachment inquiry.

Meadows declined to discuss the deposition, but acknowledged the tension.

“There is a great frustration among some of my Democratic colleagues because I know the rules extremely well,” he told The Daily Beast.

Schiff’s office declined to comment.

Tuesday’s tensions underscored a growing fear among Democrats that Republicans may use parliamentary maneuvers to cast doubt on the whistleblower’s complaint and disrupt future private and public impeachment hearings.

Top congressional Democrats, including members of the Intelligence and Judiciary Committees, have been meeting privately for weeks to discuss messaging around the impeachment inquiry. And in a meeting on Tuesday morning, House Speaker Nancy Pelosi (D-CA) and other attendees discussed how to handle potential Republican efforts to reveal the whistleblower’s identity, according to two sources familiar with the talks.

A third source who was in the meeting said they were not aware of discussion about protecting the whistleblower’s identity. But the source did say that a good chunk of the discussion focused on how to handle Republican-led attempts to disrupt future public hearings, which impeachment investigators officially teed up on Tuesday. Some Democratic members have raised concerns that hearings could become chaotic political circuses with GOP lawmakers using the parliamentary rules to bog down the sessions. Republican members have used such tactics successfully during Judiciary Committee hearings led by Chairman Jerry Nadler (D-N.Y.)—most notably when Trump’s former campaign manager Corey Lewandowski spent much of his time refusing to answer questions and berating his questioners. That hearing embarrassed many Democrats and was widely viewed as a mess, underscoring the need for new direction and leadership in oversight of the Trump White House.

Going forward, the third source said, Democrats wanted to better prepare for such “stunts” by setting firm rules for hearings.

“It is going to happen at every turn, so we have to be prepared to address it,” the source said. “So we may do it through the rule. And we need to come up with a message to deal with this.”

The House Rules Committee is slated to vote on formal rules of the impeachment hearings on Wednesday, and the full House could vote on the new rules as soon as Thursday.

Meadows said that any accusation that Republicans were trying to out the whistleblower were untrue because they did not know who to actually out.

“We don’t know who the whistleblower is, so there’s no way that we can out someone that we don’t know who it is,” he said. “I do believe that we need to hear from the whistleblower, but in terms of any ability to out the whistleblower, you have to know the name of him or her first and I can assure you that there’s not a single Republican that knows the name of the whistleblower.”

Sources have told The Daily Beast a different story. According to two knowledgeable people, a top staffer to Rep. Devin Nunes (R-CA) has been circulating the identity of a person believed to be the whistleblower among House Republicans.

On Tuesday, Rep. Debbie Wasserman Schultz (D-FL) exited the deposition and railed against Republican lawmakers for seemingly spending “most of their hours” of questioning using a variety of tactics to try to get Vindman to reveal the whistleblower’s name. She said that Republicans had been “repeatedly halted” from asking about the whistleblower during the session.

“It certainly appeared they were trying to make sure they could put a universe of individuals who had been communicated with on the table,” Wasserman Schultz told The Daily Beast during a break in the deposition.