Former national security adviser retired Lt. Gen. Michael Flynn is under Pentagon investigation for taking payments from the Russian government.
The House Oversight Committee, which is also investigating the former general for potential wrongdoing, revealed the new information.
"These documents raise grave questions about why Gen. Flynn concealed the payments he received from foreign sources after he was warned explicitly by the Pentagon," said Democratic Rep. Elijah Cummings of Maryland, the top Democrat on the House Oversight Committee, according to CNN. "Our next step is to get the documents we are seeking from the White House so we can complete our investigation. I thank the Department of Defense for providing us with unclassified versions of these documents."
Republicans on the House Oversight Committee were upset that Democrats revealed the documents before the investigation was completed.
"Though we've walked hand-in-hand with the Democrats during this investigation, this morning they broke with long-standing protocol and decided to release these documents without consulting us," said M.J. Henshaw, the spokeswoman for Republican Rep. Jason Chaffetz of Utah and the chairman of the House Oversight Committee, reported CNN.
But Democrats argued that it was appropriate to release the documents, which include a copy of a check Flynn received from RT, a Russian-government owned broadcasting network and news organization, in December 2015.
"We consulted with them extensively over the past several weeks as part of the process of working with the Pentagon to prepare unclassified versions of the documents for public release, and they were included in multiple telephone and email communications with the Pentagon," Cummings spokeswoman Jennifer Werner said. "We informed them this morning that we would be releasing these documents today. Our internal committee protocols call for consultation, not consent."
Flynn was reportedly paid $45,000 from RT, according to CNBC.
But new documents reveal that Flynn might not have followed Pentagon protocol because he did not request permission before accepting payment from a foreign government.
According to CNN, he was warned about accepting payments from foreign governments when he retired in 2014.
Like many other former U.S. government officials, including former CIA Director Michael Hayden, Flynn accepted speaking fees through Leading Authorities, LLC, a Washington D.C. public speaker agency, according to CNBC.
Many former government officials, including Hayden and Stanley McChrystal, the former former Commander of U.S. & International Forces in Afghanistan, are represented through Leading Authorities, according to the agency's website.
Hayden's listed speaking fees to speak in Europe or Asia are between $55,000 and $75,000, according to the Leading Authorities website.
McChrystal's fees are not listed.