Congressional Democrats are investigating whether Dmytro Firtash gave money to Rudy Giuliani's associates.
Two of Giuliani's associates have been charged with making illegal campaign contributions to President Donald Trump and GOP lawmakers.
According to Politico, Lev Parnas and Igor Fruman are two Americans from Eastern Europe.
Firtash is a Ukrainian natural gas oligarch with ties to organized crime.
He's accused of skimming money from the country’s state-owned natural gas company.