Flynn didn't register and wrote an op ed for Erdogan of Turkey

A business associate of a Turkish client of retired Lt. Gen. Michael Flynn testified before a federal grand jury last week, according to a new report which helps shed light on why Flynn is being investigated by special counsel Robert Mueller.

But we have the Citizens United decision which should certainly allow Flynn to lobby. Flynn didn't register as an agent for a foreign government. But the Citizens United was neutral, it cannot prevent foreign owned corporations from lobbying.  Flynn actually went through a foreign corporation as his direct employer.  Seems awfully sketchy.