Two men accused of an illegal political finance scheme with two associates of President Donald Trump's personal lawyer Rudy Giuliani pleaded not guilty Thursday in federal court in New York.

At the arraignment of the men, David Correia and Andrey Kukushkin, federal prosecutor Nicolas Roos said, "I think it's fair to characterize the government's investigation as ongoing" when the judge asked Roos whether he expected a superseding indictment to be filed in the case.

Since the case was revealed last week, multiple reports have said that the U.S. Attorney's Office for the Southern District of New York is investigating Giuliani's relationship with the two other defendants in the case — his clients and associates Igor Fruman and Lev Parnas.

Fruman and Parnas did not appear at Thursday's arraignment. They are due to be arraigned in New York next Wednesday.

Both Fruman and Parnas have been helping Giuliani to try to uncover information about former Vice President Joe Biden and his son Hunter Biden's relationship with a Ukraine natural gas company.

Before they were criminally charged, Fruman and Parnas were subpoenaed by the House of Representatives for documents and testimony related to the House's impeachment inquiry of Trump.

Trump faces possible impeachment for pressuring Ukraine to investigate Biden while he was withholding military aid to the Ukraine.

Afer Thursday's hearing, Kukushkin was released on bail of $100,000 cash, and additional security from $900,000 worth of real estate.

The other defendant, Correia, previously been released on bail for $250,000.

Kukushkin and Correia are accused of using money from a Russian national to influence politicians in their effort to launch a recreational marijuana business in Nevada. It is illegal for foreigners to contribute to U.S. politicians.

Fruman and Parnas, who were arrested last week at Dulles International Airport with one-way tickets to Europe, are also accused of the alleged scheme related to the marijuana business.

Fruman and Parnas, who are associates and clients of Giuliani, additionally are accused of funneling illegal foreign contributions to a pro-Trump political action committee as well as to a member of Congress believed to be former Rep. Pete Sessions, R-Texas, and of making false statements to the Federal Election Commission.

The Wall Street Journal reported Tuesday that a federal grand jury in New York issued a subpoena to Sessions seeking records and other information on his dealings with Giuliani and to Fruman and Parnas.

Fruman was freed on Wednesday night on bond. Parnas remains in custody, unable to meet his bail conditions.