During the visit, Flynn, a retired lieutenant general who advised Donald Trump's presidential campaign, dined with Russian President Vladimir Putin.
"General Flynn had a duty and an obligation to seek and obtain permission to receive money from foreign governments," Jason Chaffetz, the Republican Chairman of the House Oversight Committee told reporters.
"It does not appear to us that that was ever sought, nor did he ever get that permission," he said.
Flynn was forced to resign on Feb. 13 for failing to disclose talks with Sergei Kislyak, the Russian ambassador to the United States, about U.S. sanctions on Moscow and misleading Vice President Mike Pence about the conversations, which occurred in December before Trump took office.
He is a subject in investigations by intelligence committees in the House and Senate, as well as the Federal Bureau of Investigation, into allegations that Russia meddled in the 2016 U.S. election. Russia has denied the allegations, which have cast a shadow over the first 100 days of Trump's presidency. [nL2N1H70WK]
In addition to those probes, the oversight panel is looking into whether Flynn fully disclosed payments from Russian, Turkish or other foreign sources.
"As a former military officer, you simply cannot take money from Russia, Turkey or anybody else. And it appears as if he did take that money. It was inappropriate and there are repercussions for the violation of law," Chaffetz said.
He said the Army and Defense Department's inspector general would need to make a final determination.
"If that money was received by General Flynn, and we believe that it was, that money needs to be recovered," Chaffetz said.
There was no immediate response to a request for comment from Flynn's attorney.
Representative Elijah Cummings, the top Democrat on the House oversight panel, said it also appeared as if Flynn had not fully disclosed the payments after the fact as required, noting that a failure to do so would be a felony that could lead to fines and a prison sentence of up to five years.
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