Ukraine's President Volodymyr Zelenskiy and U.S. President Donald Trump hold a bilateral meeting on the sidelines of the 74th session of the United Nations General Assembly (UNGA) in New York City, New York, U.S., September 25, 2019. REUTERS/Jonathan Ernst

A second whistleblower has come forward with concerns about President Donald Trump's dealings with Ukraine.

This whistleblower has first-hand knowledge of allegations listed in a previous whistleblower's complaint, the lawyer representing this person, Mark Zaid, told ABC News on Sunday.

The previous whistleblower's complaint triggered an official impeachment inquiry in the House of Representatives. Zaid works for Compass Rose Legal Group, a law firm that focuses on representing whistleblowers and also represents the first whistleblower.

Zaid said the whistleblower spoke to the intelligence community's inspector general.

Andrew Bakaj, also an attorney with Compass Rose, confirmed in a statement "that my firm and my team represent multiple whistleblowers."

"I can confirm that my firm and my team represent multiple whistleblowers in connection to the underlying August 12, 2019, disclosure to the Intelligence Community Inspector General," Bakaj tweeted. "No further comment at this time."

Democrats have accused Trump of abusing power by suggesting in a July 25 phone call with Ukraine's president that the country investigate Joe Biden, a potential 2020 rival, and his son Hunter. House Speaker Nancy Pelosi has said the White House's initial efforts to suppress the contents of the call, as described in the whistleblower complaint, amount to a "cover-up."

White House press secretary Stephanie Grisham said in a statement Sunday that "It doesn't matter how many people decide to call themselves whistleblowers about the same telephone call — a call the President already made public — it doesn't change the fact that he has done nothing wrong."

Secretary of State Mike Pompeo said Saturday that the State Department would comply with Congressional subpoenas and hand over documents as required by law, but criticized the investigation, saying there were "clearly politics" involved. House Democrats on Friday subpoenaed the White House for documents they say are central to the investigation.

Trump on Saturday attacked the second whistler blower as part of a series of tweets defending himself amid the impeachment inquiry.

"The first so-called second hand information 'Whistleblower' got my phone conversation almost completely wrong, so now word is they are going to the bench and another 'Whistleblower' is coming in from the Deep State, also with second hand info," Trump wrote. "Meet with Shifty. Keep them coming!

The president's reference to "shifty," or Rep. Adam Schiff (D-Calif.), chair of the House Intelligence Committee, seemed to reference Republican efforts to discredit the Democrats' impeachment inquiry and the first whistleblower.

Trump on Thursday also publicly urged China to investigate Biden, a move that pushed back against critics who argue that such a request is a blatant violation of the presidency. His request to China came as the first witness was interviewed by House investigators as part of the ongoing impeachment inquiry.