Federal prosecutors from the Southern District of New York have issued subpoenas to people fundraising for President Donald Trump as they dig up information about Rudy Giuliani and his associates, Lev Parnas and Igor Fruman.

According to the New York Times, the subpoenas are an extension of the probe into Parnas and Fruman, who were arrested on campaign finance charges last month. Some of the subpoenas were issued to the lobbying firm of top Trump fundraiser Brian Ballard and two people who raise money for the Trump-aligned super PAC America First Action.

According to CNN, FBI agents also knocked on the doors of other players involved in Republican campaigns.

The same prosecutors are also investigating Giuliani’s business dealings in Ukraine, and his name was one was on of the subpoenas. That subpoena was issued to a businessman who Parnas approached for an investment to help pay Giuliani to consult for his company, Fraud Guarantee. The businessman in question never coughed up the money.

While the closely related investigations circle Giuliani, his name has been bandied about frequently in the impeachment inquiry hearings, as witnesses describe his pivotal role in the Ukraine pressure campaign. Fruman and Parnas also played key roles, especially in bringing about the ouster of former Ambassador to the Ukraine Marie Yovanovitch.

Giuliani has defied his House subpoena and denied all wrongdoing. He also lashed out at the Republicans’ staff attorney Wednesday, when the lawyer brought up a line of questioning trying to paint Giuliani as a long actor operating in Ukraine based on his own personal business interests.