Paul Manafort, the former campaign manager for Donald Trump, has had his bail revoked by a Washington DC judge and has been ordered to jail pending trial.
Robert Mueller, who is investigating alleged Russian election interference, accuses him of trying to tamper with potential witnesses before the trial.
Paul Manafort was accused of using encrypted mobile phone apps to contact people in breach of his bail terms.
He faces charges of tax fraud, money laundering, and illegal lobbying.
US District Judge Amy Berman Jackson said on Friday that Mr Manafort had “abused the trust placed in you” and treated the court proceedings as “just another marketing exercise”.
“This is not middle school, I can’t take his cell phone,” she added, according to US media.
Mr Trump said it was “very unfair” and called it “a tough sentence”, although Mr Manafort has not gone on trial yet.
In a separate development, Mr Trump’s lawyer Rudy Giuliani said that there is a “good chance” that the president will decide next week whether he will sit down for an interview with Mr Mueller.
But the former New York mayor advised that Mr Trump should not co-operate, saying: “Why would he get interviewed in a corrupt investigation?”
What is Paul Manafort charged with?
Mr Manafort’s trial on charges of money laundering and illegal lobbying is due to begin in September.
He is accused of laundering more than $30m (£22m) and failing to disclose his lobbying efforts to the Department of Justice.
His other trial – on tax fraud charges – is due to start next month.
The indictments are not connected with allegations of collusion between Russia and the Trump campaign during the US election in 2016.
If Mr Manafort is convicted, he faces years in jail.
Last week, Mr Manafort and his aide, Konstantin Kilimnik, were charged with witness tampering.
Mr Kilimnik, who denies having ties to Russian intelligence, was a long-serving employee of Mr Manafort’s political consultancy.
Mr Manafort, who resigned as chairman of the Trump campaign in August 2016, has been under house arrest since he was charged last October.
He had been confined to that Alexandria, Virginia home since his arrest, and was forced to wear a GPS monitoring device.
He was indicted after FBI agents seized documents from his home in a pre-dawn raid in July last year.