U.S. Supreme Court judges asked prosecutors a slew of tough questions Tuesday about the conviction of Conrad Black, an encouraging sign for the jailed media baron trying to reclaim his freedom.

Conrad Black arrives at a federal court in 2007 for sentencing on his fraud and obstruction of justice convictions. (M. Spencer Green/Associated Press)

At a one-hour hearing on Tuesday, the top U.S. court heard challenges to the "honest services" fraud law, a contentious act that critics argue is too vague and has been used to make a crime out of mistakes, minor transgressions and ethical violations.

Several justices, including the court's newest member, Sonia Sotomayor, appeared to agree in broad terms with the idea that the "honest services" law is too vague to be useful.

The 28-word law makes it illegal for officials, executives and others to scheme to deprive those they serve and possibly others of "the intangible right to honest services." The concept crept into the legal lexicon in the 1980s, when the U.S. Congress amended fraud statutes.

Justices peppered federal government lawyer Michael Dreeben with questions on the law's use in recent cases, including Black's.

Justice Stephen Breyer was particularly forceful, saying he worries the Obama administration's interpretation of the law makes criminals out of vast numbers of U.S. workers, including possibly employees who read a daily horseracing newspaper on the job.

"There are 150 million workers in the United States," Breyer said. "I think 140 of them would flunk the test."

The court is hearing three cases this term in which defendants are challenging the use of the law against them.

Former newspaper mogul Conrad Black, who has served nearly 22 months of a 6½-year prison term, and former Alaska legislator Bruce Weyhrauch, who has been indicted but not tried, are asking the court to throw out the prosecutions against them.

Black was unable to attend Tuesday's proceedings because he is in a Florida prison and cannot be released on bail. Family members, including his daughter, Alana, were in attendance in the courtroom.

Former Enron chief executive Jeffrey Skilling, convicted in 2006 on conspiracy, securities fraud, insider trading and lying to auditors involving the company's collapse in 2001, will have his case heard in the spring. He has said the honest services law is unconstitutionally vague.

A former Illinois governor, George Ryan, was convicted of honest services fraud, and another, Rod Blagojevich, faces the same charge, among others.

Former Alabama Gov. Don Siegelman and ex-HealthSouth chief executive Richard Scrushy also are appealing their honest services fraud convictions to the Supreme Court.

The court is not expected to rule on any of these cases until well into 2010.

The defendants appear to have another powerful ally on the bench in Justice Antonin Scalia. Urging the court in February to take a case to resolve questions about the law, Scalia said it "invites abuse by headline-grabbing prosecutors in pursuit of local officials, state legislators and corporate CEOs who engage in any manner of unappealing or ethically questionable conduct."

Former Enron CEO Jeffrey Skilling, right arrives at the federal courthouse during his trial in 2004. (David J. Phillip/Associated Press)

Black and two other former executives were convicted of depriving the Hollinger International media empire of their faithful services as corporate officers. They want the honest services convictions overturned claiming they intended no economic harm to the company, which once owned the Chicago Sun-Times, the Daily Telegraph of London, the Jerusalem Post and hundreds of community papers across the United States and Canada.

Central to the case is $5.5 million US that the defendants say were management fees they were owed and were trying to collect in such a way that they would not have to pay Canadian income tax. The U.S. government claims the money belonged to the company's shareholders.

With files from The Canadian Press