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.
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 whistleblower also says that Flynn assured Copson that USA sanctions on Russian Federation that could block the nuclear project would be "ripped up" once Trump was inside the White House.
House Oversight Chairman Trey Gowdy (R-SC) showed no interest Wednesday in further investigating claims a whistleblower brought to the committee's Democrats about promises former National Security Advisor Mike Flynn allegedly made to a business associate about gutting Russian Federation sanctions that been hindering the associate's business project. "This is going to make a lot of very wealthy people".
"I am going to celebrate today" Copson said, according to the whistle-blower. He also lied when he said he did not recall a follow-up conversation with the ambassador, who said that "Russia had chosen to moderate its response to those sanctions as a result of Flynn's request".
A lawyer for Mr Flynn, who was sacked after only 24 days as Mr Trump's national security adviser, declined to comment.
"I do not bring this whistle-blower to your attention lightly", Cummings said. But he asked Gowdy to issue a subpoena to the White House for documents related to Flynn, saying that the committee has "credible allegations" that Flynn "sought to manipulate the course of global nuclear policy for the financial gain of his former business partners". Mr. Cummings said that Mr. Gowdy should subpoena Mr. Flynn, Mr. Copson and four others to testify before the panel.
"These grave allegations compel a full, credible, and bipartisan congressional investigation", Mr Cummings wrote in the letter to Mr Gowdy, a South Carolina Republican, which outlines the information provided by the whistle-blower.
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.
"When the whistle-blower asked why the United States needed to be involved in a Middle East nuclear project, Mr Copson explained that the USA would provide military support to "defend these installations", the letter said.
Mr Copson showed his phone with the text message to the whistle-blower, who saw that the time stamp of the message was 12:11, but didn't read the text.
The whistleblower came forward this summer and spoke to the committee about attending an inauguration party and meeting Alex Copson, managing partner of ACU Strategic Partners.
Flynn had worked as a consultant for ACU Strategic Partners, the group pushing the proposed nuclear deal, in 2015 and 2016.