Maryland Rep. Elijah Cummings, the ranking Democrat on the Committee on Oversight and Government Reform, said Wednesday the whistleblower's allegations raise concerns that Flynn improperly aided the nuclear project after joining the White House as one of Trump's top national-security officials.
"Mike has been putting everything in place for us", Copson reportedly told the whistleblower.
Mr Cummings said the whistle-blower detailed a business effort that was aimed at boosting investment in the Middle East.
The episode indicates that Trump officials had planned to jettison sanctions that the Obama administration had imposed on Russian Federation.
Flynn, who pleaded guilty last week to lying to the Federal Bureau of Investigation, was communicating with former business associates "within minutes" of Trump's inauguration, according to the letter - reassuring them Russian investments would soon be available as the Trump administration lifted sanctions.
The whistleblower, who provided his account to Cummings in June, said he was with Alex Copson, managing partner of ACU Strategic Partners, a key Flynn ally on the nuclear project, on January 20, Inauguration Day.
Cummings responded to Gowdy's letter with a letter Thursday that called Gowdy's refusal to investigate the whistleblower's claims "astonishing".
The project in question - promoted by a group of former senior United States military officers, and often described as a "Marshall Plan" of sorts - would involve U.S. companies working with Russian companies to build and operate nuclear plants in the Middle East, and export spent fuel from those plants.
The company did not respond to a request for comment Wednesday.
Cummings wrote that Mueller's office had asked him to hold back the information until "they completed certain investigative steps" - which apparently have now been concluded.
"Your letter seems to resort to desperate and baseless jurisdictional excuses to avoid conducting oversight in an apparent attempt to protect President Trump and his Administration", Cummings said while pointing out "inaccuracies" in Gowdy' letter.
"I do not bring this whistle-blower to your attention lightly", Mr. Cummings said.
Mr Copson explained that Flynn was making sure that sanctions were going to be "ripped up" as one of the first orders of business and this would allow money to start flowing to the project.
The whistle-blower told Mr Cummings that he was attending an inaugural event on Jan 20, where he met one of Flynn's key allies on this project, Mr Alex Copson, who is described as a managing partner of ACU Strategic Partners, and was working with Flynn to promote the joint project with Russian Federation to build nuclear reactors in the Arab world. Now Cummings wants to look into the matter.
ACU Strategic Partners paid for Flynn to travel to Israel and Egypt in 2015 to promote the nuclear project, paying him a fee of $25,000, according to a letter Copson sent the committee.
The letter from Cummings concluded with a request to issue subpoenas for "all documents and communications referring or relating" to Flynn's foreign contacts during the Trump campaign, the transition period and his brief time as national security adviser.