In a letter from Rep. Elijah Cummings (D-Md.) to Rep. Trey Gowdy (R-S.C.), the chairman of the House Oversight Committee, Cummings claims the whistleblower said Flynn messaged a former business colleague, whom he worked with on a project with Russian Federation to "build nuclear power plants in the Middle East", that the plan was "good to go" because the sanctions would be "ripped up" as one of Trump's first acts in office.
Flynn pleaded guilty on Friday to lying to the Federal Bureau of Investigation about his discussions with the Russian ambassador about sanctions during the transition.
It is alleged that while sitting a few yards away from the podium where President Trump was delivering his inaugural address on 20 January, Mr Flynn sent the texts to Alex Copson, managing partner of ACU Strategic Partners, a United States nuclear power consultancy.
The whistleblower also alleges that Copson said Flynn had assured him that USA sanctions on Russian Federation would be "ripped up" as soon as Trump was inside the White House.
One of them, a proposed venture to help Middle Eastern nations build nuclear power plants with assistance from Russian Federation and the USA, garnered significant press attention. It gave Flynn a potential monetary incentive to get sanctions imposed on Russian Federation during the Obama administration lifted immediately.
Elijah Cummings, the ranking Democrat on the Committee on Oversight and Government Reform, said 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.
In return, the incoming White House would review the Obama sanctions, Flynn told him, according to the court documents filed by special counsel Robert Mueller's office.
Flynn attempted to "manipulate the course of global nuclear policy for the financial gain of his business partners", and assured a business partner the USA would relax sanctions once he worked in Trump's White House, Cummings wrote to House Oversight Chairman Trey Gowdy, R-South Carolina.
The letter says Flynn blamed Obama for having 'f***** everything up in my nuclear deal with the sanctions'.
Cummings told Gowdy in his letter that he found the witness "authentic, credible and reliable".
The whistleblower's story to Cummings starts January 20, Inauguration Day, at an event in D.C. The whistleblower encountered a business partner of Flynn's, Alex Copson of ACU Strategic Partners, which was working on building the reactors.
The witness told Cummings and committee investigators that Copson shared a text message he had just received from Flynn, who was on stage at the Capitol during Trump's speech.
"Mike has been putting everything in place for us", Copson told the whistleblower. "I am going to celebrate today", and added, according to the whistleblower: "This is going to make a lot of very wealthy people".
The whistleblower was "extremely uncomfortable" with the situation, and made notes about it and Copson's name.
It also raised fresh questions on what Trump knew about Flynn's business plans as he appointed the retired three-star general his national security adviser.
President Trump's personal White House lawyer, Ty Cobb, also declined to comment.