Federal investigators in the United States have accused President Donald Trump’s former campaign manager, Paul Manafort, of tampering with potential witnesses while on bail, reported The New York Times on Monday. The development precedes a hearing in the bank and tax fraud case against him.

United States Special Counsel Robert Mueller, who is investigating an alleged collusion between the Trump campaign and Russia in the 2016 presidential election, said Manafort had contacted witnesses by phone and encrypted messages, seeking to secure “materially false testimony”, reported BBC.

Mueller asked the judge overseeing the case in United States District Court for the District of Columbia to revoke or revise an order releasing Manafort ahead of his trial, Reuters reported. Manafort was released to home confinement after his arraignment in October.

Manafort is indicted in federal courts in Washington and Virginia with allegations of money laundering, failing to register as a foreign agent working on behalf of Ukraine’s former pro-Russia President Viktor Yanukovych, bank and tax fraud. Manafort has pleaded not guilty to all the charges.

This is the second time prosecutors have complained about Manafort’s behaviour while awaiting trial, reported The Washington Post. After he was released to home confinement, federal investigators said they intercepted emails showing Manafort helped write an opinion piece defending his actions in Ukrainian publications.