The Pentagon inspector general is investigating whether a sacked Trump adviser took money from foreign governments without necessary approval.
Michael Flynn was warned in 2014 about declaring foreign funds, a year before he appeared on Russia television and was paid $45,000, documents show.
Mr Flynn's links to Russia are being scrutinised by the FBI and two congressional committees.
A lawyer for Mr Flynn said the Pentagon was aware of one of his paid speeches.
Congressional members now want the Army to determine whether he broke the law.
The inspector generals' letters also show that the agency found no evidence that he sought prior approval.
In a letter sent to the acting secretary of the Army, Republican House Oversight Committee chairman Jason Chaffetz requested that "in light of these apparent violations" the Army establish a way for Mr Flynn to repay the hundred of thousands of dollars that he received from the governments of Russia and Turkey.
The committee's ranking Democratic member, Elijah Cummings, also released a 2014 document given to Mr Flynn by his old employer, the Defense Intelligence Agency (DIA), which outlines his ethics restrictions - including a prohibition on accepting payments from foreign governments.
He also released a redacted letter from the DIA saying they could not "locate any records of LTG Flynn seeking permission or approval for the receipt of money from a foreign source".
But a lawyer for Mr Flynn said that the redacted sections in the letter confirm that he had actually provided two briefings to defence officials, one before and one after the event.
"The Department was fully aware of the trip," lawyer Robert Kelner said. He also calling upon the DIA and the committee to release the full unredacted note.
Earlier this week, the White House refused to release Mr Flynn's forms that he filed in order to obtain a White House security clearance.
Mr Flynn received more than $33,000 (£25,700) from Russian broadcaster RT for giving a speech at its Moscow gala in 2015. He was seated at a table next to the Russian president.
He also received more than $500,000 from Turkey for lobbying he undertook on their behalf in Washington after leaving the Defense Intelligence Agency in August 2014, and before joining the Trump administration.
His lawyer has said that he wants immunity to testify before Congress on alleged Russian election meddling.
Mr Flynn quit as national security adviser in February after failing to disclose to the White House his conversations with the Russian ambassador to Washington.