Lawyers representing the whistleblower behind the explosive complaint involving President Trump's efforts to persuade Ukraine's president to investigate former Vice President Joe Biden and his son Hunter Biden expressed concern for their client's safety in a letter to lawmakers released Sunday.

In a letter to Senate Intelligence Committee Chairman Richard Burr (R-N.C.), House Intelligence Committee Chairman Adam Schiff (D-Calif.) and others, lawyers representing the whistleblower said they had "serious concerns for our client's personal safety, as well as for others connected to this matter." They called on lawmakers "to speak out in favor of whistleblower protection and reiterate that this is a protected system where retaliation is not permitted, whether direct or implied."

The lawyers also attached correspondence with acting Director of National Intelligence Joseph Maguire thanking him for his supportive words during his testimony and expressing concerns for their client.

"60 Minutes," which first obtained the letter, originally reported that the contents suggested the whistleblower was under federal protection. However, lawyer Mark Zaid said in a statement to The Hill that the news outlet "completely misinterpreted the contents of our letter."

The whistleblower's complaint, which was released to the public on Thursday, is at the center of House Democrats' impeachment inquiry.

Trump and his allies have sought to discredit the complaint and the whistleblower behind it.

The president on Sunday tweeted that the person who filed the complaint should be outed and that they will face "Big Consequences."

Little is known about the whistleblower, who, according to the complaint, was not a direct witness to the conversation but was told about it by White House colleagues.

The president's camp has zeroed in on the whistleblower not being directly privy to the call between Trump and his Ukrainian counterpart, Volodymyr Zelensky, as a disqualification of the complaint.

The partial transcript of the call confirms the whistleblower's claim that Trump pressed Zelensky to investigate the Biden family.

The New York Times has reported the whistleblower is a CIA officer who is currently working at the agency's headquarters in Langley, Va.

EDITOR'S NOTE: This story has been updated with a statement from the lawyer and to clarify the contents of the letter.