Within minutes of Trump's inauguration in January, Flynn informed his former associate that the plan to work with Russian Federation to build nuclear reactors in the Middle East was "good to go", because Flynn was ensuring the sanctions would be "ripped up" as one of Trump's first orders of business.
According to the account detailed in the letter, the whistle-blower had a conversation on Inauguration Day with Alex Copson of ACU Strategic Partners, a company that hired Mr. Flynn in 2015 as an adviser to develop a plan to work with Russian Federation to build nuclear power plants throughout the Middle East. Mr. Flynn served as an adviser until June 2016.
In June, Newsweek revealed that while he was an adviser to Trump, Flynn had done work for a consortium led by Copson and former senior US military officials to build nuclear power plants in the Middle East in a partnership with a Russian state-owned energy contractor.
The congressman, Rep. Elijah Cummings, outlined the whistleblower's allegations in a letter to House Oversight Committee Chair Rep. Trey Gowdy earlier this week. He called for a bipartisan investigation.
On Inauguration Day, Flynn apparently texted Copson that the power plant venture was "good to go", according to the whistleblower.
Flynn had assured his former associate that USA sanctions against Russian Federation would immediately be "ripped up" by the Trump administration, a move that would help facilitate the deal, the associate told the witness.
Mr. Cummings said Mr. Gowdy should subpoena the White House and the Flynn Intelligence Group, Mr. Flynn's former company, for documents that the House committee had requested in March but had not yet been provided.
An attorney for Flynn did not respond to a request for comment from CNBC.
Reuters last week published documents that showed Copson and other plan proponents believed they had Flynn and Trump in their corner. Copson added that "this is going to make a lot of very wealthy people".
The whistleblower noted the time of the message, 12:11 pm-during Trump's inaugural speech, but didn't read the content. Copson told the whistleblower, "Mike has been putting everything in place for us".
The witness told congressional investigators that he was "extremely uncomfortable" with the conversation, Cummings wrote, and took brief notes about the discussion during the inaugural event.
Flynn's financial disclosure did not cite those payments, but he did report that until December 2016, he worked as an adviser to two other companies that partnered with Copson's firm.
Copson could not be reached for comment. "I have spoken to this whistleblower, and I find this person to be authentic, credible, and reliable", Cummings wrote.