Nunes did not share the information with Democratic Rep. Adam Schiff, the House Intelligence Committee's ranking member, before his press conference, NBC News reported. The pair has recently held joint news conferences about the committee's Russia probe.
In a statement late Wednesday afternoon, Schiff said members of the committee only learned about the findings Nunes discussed when he held the press conference. Schiff said he talked to Nunes and "expressed (his) grave concerns with the chairman that a credible investigation cannot be conducted this way."
The information Nunes referenced Wednesday is not related to a criminal investigation and "appears to be all legally collected foreign intelligence," the California Republican said. The intelligence committee chairman said an unidentified intelligence community source gave him the information, but did not go into more detail.
He added that "additional names" of Trump transition officials were "unmasked," or revealed improperly, without saying who those people are. Nunes said the unmasking "really bothered" him.
After briefing Trump at the White House later on Wednesday, Nunes told reporters the revealing of names "goes beyond" former National Security Advisor Michael Flynn. Information released about Flynn's calls with the Russian ambassador to the U.S. contributed to his resignation last month.
Schiff said in his statement that "most of the names in the intercepted communications were in fact masked."
The congressmen both reiterated that they see no evidence of a physical wiretap at Trump Tower. Nunes said he did not know if any of the information he referenced was collected from inside the New York building.
Trump has stood by his unsubstantiated claim that the Obama administration wiretapped Trump Tower even after the FBI director and bipartisan chairmen and the Senate and House Intelligence communities said they saw no evidence to back the accusation.
Still, Trump told reporters Wednesday he felt "somewhat" vindicated by Nunes' briefing. The White House has aimed to change the interpretation of Trump's tweets since he sent them earlier this month, saying he may have referred to broader surveillance activities.
After he briefed Trump, the congressman said he thought it was appropriate to do so, despite concerns of interference with the Russia investigation. The information did not relate to the probe into Moscow's alleged meddling, he said.
"I'm not drawing any conclusion, I'm just telling the president what exists in intelligence reports," Nunes said outside the White House.
White House press secretary Sean Spicer said Wednesday he did not worry Nunes' meeting with Trump would create the appearance that the White House is interfering in the investigation.
Nunes said he briefed House Speaker Paul Ryan about the findings and also spoke to the directors of the Central Intelligence Agency and National Security Agency.