Mr Nunes calls the charges “entirely false” and “politically motivated”.
The head of a key US congressional investigation into alleged Russian hacking has temporarily stepped down amid an ethics inquiry into him.
House Intelligence Committee chairman Devin Nunes is now himself under investigation by the House Ethics Committee.
The panel is looking into claims that the Republican disclosed classified intelligence.
Mr Nunes called the charges “entirely false” and “politically motivated”.
Representative Mike Conaway will take control of the Russia investigation.
Mr Nunes said his decision came after “several leftwing activist groups have filed accusations against me with the Office of Congressional Ethics”.
He added he would continue to fulfill his other responsibilities as chairman and has requested to speak to the ethics panel “in order to expedite the dismissal of these false claims”.
Democrats have criticised Mr Nunes for his handling of the inquiry, which is also looking at possible links between the Trump campaign and Moscow.
What did Mr Nunes allegedly do wrong?
The House Ethics Committee said in a statement on Thursday: “The Committee is aware of public allegations that Representative Devin Nunes may have made unauthorised disclosures of classified information, in violation of House rules, laws, regulations, or other standards of conduct.”
Watchdog groups Democracy 21 and Citizens for Repsonsibility and Ethics in Washington had asked the House ethics panel to investigate any possible violations by Mr Nunes.
Mr Nunes’ political enemies have accused him of helping the White House to divert attention from an FBI announcement that they were investigating alleged links between the Trump team and Russian officials.
Mr Nunes has acknowledged making an after-dark trip to the White House grounds last month that even his own aides were apparently unaware of.
The next day he hastily announced at a news conference that he had learned post-election communications of Mr Trump’s team had been monitored by intelligence agencies as they snooped on foreign officials.
He expressed alarm that information about the then-incoming president’s aides were swept up in US intelligence reports.
Mr Nunes’ Democratic colleagues on the panel were furious that he had not shared such information with them before going public.
In the face of much scepticism, Mr Nunes maintains White House officials were not his original source for the claims.
The California Republican reportedly apologised for the incident.
But Democrats questioned whether the investigation into Russia’s alleged role in the election could proceed objectively.
Russia reboot – Anthony Zurcher, BBC News, Washington
It’s never a good sign when the investigator becomes a bigger story than the investigation.
Such was the case with Congressman Devin Nunes, with his shifting explanations for where and how he acquired sensitive intelligence documents, his decision to keep details from his fellow intelligence committee members, his apparent behind-the-scenes co-ordination with White House sources and his penchant for dramatic press conferences.
All this made him a liability for Republican congressional leadership and the White House. Now he is, at least temporarily, out of the picture.
He may blame an ethics complaint filed by “leftwing activist groups” for forcing the move, but there’s little doubt that many Republicans are breathing a sigh of relief. Mr Nunes, at times, seemed out of his depth on the big political stage.
The committee’s investigations effectively had been ground to a halt by partisan bickering, and this move is a first step toward rebooting the efforts.
It may be too late, however, as the concurrent Senate intelligence committee investigation has launched more smoothly and with a greater show of bipartisan co-operation.
Members of the House of Representatives often complain of being viewed as the “baby brother” to the upper chamber. The dual Russia probes haven’t done much to dispel that notion.
What’s been the reaction?
House Speaker Paul Ryan said he fully supported Mr Nunes’ decision.
Mr Ryan said he trusts Mr Nunes, describing him as “eager to demonstrate to the Ethics Committee that he has followed all proper guidelines and laws”.
But he added that the inquiry “would be a distraction” for the House Intelligence Committee’s investigation.
Representative Adam Schiff, a ranking Democrat on the House Intelligence Committee, said he respected Mr Nunes’ decision.
“We have a fresh opportunity to move forward in the unified and nonpartisan way that an investigation of this seriousness demands,” he said at a news conference on Thursday.