A federal judge has scheduled a hearing for June 15 on whether to revoke bail for Paul Manafort, President Donald Trump's former campaign chairman, after federal prosecutors alleged that he tried to tamper with potential witnesses while on pretrial release.

Judge Amy Berman is expected to rule at the hearing on whether Manafort will have to go to jail pending his trial in connection with special counsel Robert Mueller's investigation of alleged Russian interference in the 2016 presidential campaign, or whether the terms of his bail are further restricted.

Federal prosecutors asked Judge Berman to revoke bail in a motion filed in U.S. District Court in Washington, D.C. Monday night. According to an FBI affidavit included with the motion, Manafort used encrypted messaging applications in February to try to reach two unnamed business partners who could be witnesses to his alleged fraud and money laundering. The judge has ordered the FBI agent who filed the declaration regarding the messaging to be in court and available to testify if necessary.

In a statement, Manafort spokesperson Jason Maloni said, "Mr. Manafort is innocent and nothing about this latest allegation changes our defense. We will do our talking in court."

Judge Berman has asked Manafort's lawyers to respond to the prosecutors' filing by June 8.

One of the potential witnesses said he believed Manafort's outreach was an attempt to "suborn perjury" or to instruct him to lie after a superseding indictment was filed in February against Manafort. The superseding indictment was filed after his co-defendant, Rick Gates, a former Trump campaign aide, pleaded guilty to conspiracy and lying to Mueller's investigators.

Gates and Manafort had been indicted together in October in Washington on charges related to their lucrative lobbying work for pro-Russian Ukrainian political figures.

After Gates agreed to cooperate with investigators in February, Manafort pleaded not guilty to the superseding indictment, which accuses him of having secretly recruited and funded a group of former European politicians to lobby in the United States on Ukraine's behalf.

Gates and Manafort helped to create the Hapsburg Group in 2011 to remain "under the radar" to speak on behalf of Ukraine while secretly being paid millions of euros, according to the government. Subsequently, the company disseminated ghostwritten articles in the U.S. media and arranged meetings with members of Congress and the executive branch, the affidavit said.

Manafort's former son-in-law and business partner, Jeffrey Yohai, pleaded guilty to unrelated charges of financial irregularities and agreed to cooperate with other federal investigations, widely reported to include Mueller's inquiry.

According to Monday's FBI affidavit, two people who were part of a broader effort to lobby on behalf of Ukraine told investigators that Manafort, while on bail, contacted them "in an effort to influence their testimony and to otherwise conceal evidence."

Telephone records and other documents recovered in a search of Manafort's cloud storage account corroborated the allegations, according to the FBI.

According to the FBI filing, both men told investigators that they understood that their work was to be carried out in both the European Union and the United States, but one said the message that was being sent was that if members of the Hapsburg Group were contacted by anyone, they should say their work was exclusively in Europe.

Both men said the messages from Manafort in February, both directly and through an intermediary, were intended to get messaging out to the broader Hapsburg Group.

"We should talk," Manafort said in one of the messages, according to the FBI. "I have made clear that they worked in Europe."

And as recently as April, the FBI said, one of the men got a message from a third party relaying that "my friend P" — an apparent reference to Manafort — "is looking for ways to connect to you to pass you several messages. Can we arrange that."