Conrad Black's lawyer asked a U.S. federal appeals court in Chicago to throw out the former Canadian newspaper baron's convictions.

In the sometimes-heated hearing on Wednesday, attorney Miguel Estrada argued Black was convicted by a 2007 jury under a law that has since been ruled to be mostly unconstitutional.

Estrada said Black's conviction for defrauding Hollinger International Inc. investors should be tossed because the jury put too much weight on the "honest services" laws that the U.S. Supreme Court ruled against this June.

The prosecution argued Black's conviction wasn't about the "honest services" laws but about the simple notion of theft.

Black, who was not in court, appears to be facing an uphill battle with the three judges overseeing the case.

Chicago defence lawyer Stephen Komie, who is not connected to the case, said the judges "are no friends of the defendant."

"These are people who generally support the government," he said.

Judge Richard Posner of the 7th U.S. Circuit Court of Appeals in Chicago repeatedly went after Estrada, once saying his argument "didn't make sense."

Black has served more than two years of his six-and-a-half year sentence for fraud and obstruction of justice and is now free on bail and living in Florida.

The court will also hear arguments from lawyers for Black's three co-defendants -- Peter Atkinson, John Boultbee and Mark Kipnis.

Atkinson and Boultbee were both Canadian executives of Hollinger and were sentenced to two years and 27 months respectively.

Chicago attorney Mark Kipnis, a former Hollinger employee, was given six months probation.

Komie told CTV News Channel that Black is facing "more than enough charges for a revisit to the pen."

"He could go back anytime depending on what the court rules," he added.

James Morton, a Toronto lawyer, told The Canadian Press he believes the court will throw out the fraud convictions but uphold the obstruction of justice conviction.

Black could be resentenced on the obstruction of justice conviction, which could mean he could be sent back to jail to serve out his sentence by as early as Christmas.

Or, if the appeals court dismisses all the convictions, he could be released by that time, Morton said.

Black was once head of the world's third-largest newspaper empire until he was ousted in 2003 following shareholder complaints.

Hollinger once owned the Chicago Sun-Times, the London Daily Telegraph, the Jerusalem Post and hundreds of other newspapers.