"Mike has been putting everything in place for us", Copson reportedly told the whistleblower.
"Mr. Copson explained that General Flynn was making sure that sanctions would be "ripped up" as one of his first orders of business and that this would allow money to start flowing into the project", Cummings wrote. 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".
Flynn pleaded guilty Friday to lying to the Federal Bureau of Investigation during its probe of Russian interference in the presidential election, including about conversations with Russia's ambassador to the USA about sanctions.
The whistleblower said that Copson quickly displayed what he claimed to be a text message from Flynn that appeared to have been sent during Trump's inauguration speech.
"These grave allegations compel a full, credible and bipartisan congressional investigation", Cummings wrote, according to the New York Times. It was pushed by a company that Flynn had advised during the 2016 campaign and transition, seeking to promote a joint venture with Russian Federation to build nuclear power plants in the region.
"When you took over as Chairman this summer, you refused to press the White House to comply with our bipartisan request for documents, and you disregarded new evidence we uncovered about General Flynn's secret effort to work with Russian Federation on a plan to build nuclear reactors in Saudi Arabia", he wrote.
"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.More news: Florida State Seminoles coach Jimbo Fisher to take Texas A&M coaching job
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.
Cummings said that he practiced law for a long time and has interviewed hundreds of witnesses, and he does believe the whistleblower is "very credible".
"I do not bring this whistle-blower to your attention lightly", Cummings said.
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.
Mr. Copson quickly showed the whistleblower his phone with the text message.
The witness did not specify which sanctions Flynn was referring to in his texts.
Based on the witness's account, Mr Cummings requested that Mr Gowdy issue subpoenas to White House Chief of Staff John Kelly - as a custodian of White House records - Flynn, Michael Flynn Jr, the Flynn Intel Group, Mr Copson, and others, for e-mails, text messages and other documents related to Flynn's foreign contacts and payments.
Cummings added: "They have now informed us that they have done so".