A group of senior Democratic members of the U.S. House of Representatives have asked the Defense Department to investigate whether President Donald Trump's national security adviser violated the constitution by accepting money from Russia's state-funded RT television network.
The ranking Democrats on six House committees sent the open letter on February 1.
National security adviser Michael Flynn, a retired U.S. Army general, attended a Moscow event to mark RT's 10th anniversary in 2015, sharing a dinner table with Russian President Vladimir Putin.
Flynn has admitted that he was paid to attend the event, but has refused to name the amount.
The letter states that the Defense Department has ruled in the past that the constitutional provision against accepting gifts or payments from foreign governments applies to retired officers "because they continue to hold offices of trust."
U.S. counterintelligence officials are reportedly already looking into Flynn's alleged communications with Russian officials, including Russia's ambassador to the United States, in the days immediately before Trump's January 20 inauguration.