The recent conviction of Conrad Black, who currently is serving a sentence of six-and-a-half years in a federal prison, was based upon a statute which, owing to its inherent ambiguity, has been condemned by legal scholars and has divided the federal courts in their attempt to define it. That statute is now the focus of Black’s appeal.

The statute — the “honest services” fraud statute — was enacted by Congress in 1988 in response to a Supreme Court ruling which held that the federal mail and wire fraud statutes do not cover the theft of intangible assets. To correct this problem, Congress made it a crime “to deprive another of the intangible right to good services.”

The new law came under immediate attack from legal scholars. While the paradigmatic case was clear — the corporate officer who, having taken a bribe, causes the corporation to act in a way that is against the corporation’s economic interest — the plain language of the statute went beyond this to include activity which is not typically criminal, that is, minor or unintentional breaches of fiduciary duty having no ill-effect on the company to which the duty was owed.

Compounding the problem is that the law of fiduciary duty varies between states and courts apply the law of the state of incorporation in determining when breaches of duty have occurred. This means, as has been pointed out by Professor John Coffee, that whether an individual is criminally liable could turn on a law that has “no relationship to the community in which the conduct occurred or in which the trial will occur.” Acknowledging the force of these arguments, federal courts have attempted to give coherence to the statute. The difficulty has been that with little or no guidance from the language or legislative history of the statute, the courts have invented limitations that are wide ranging and contradictory. Some courts, for example, require that the breach of fiduciary duty cause an injury to the finances or property of the company to whom the duty is owed; other courts reject this limitation but hold that the breach must also violate a state statute or that the government must prove that the victim of the fraud would have acted differently if the fraud had never taken place. Still other courts eschew any meaningful limitation.

This places corporate officers, as well as all other fiduciaries, in the position of not knowing what actions may subject them to criminal prosecution. And this, rather obviously, defies the constitutional mandate that individuals be given clear notice of what constitutes criminal conduct. “It offends reason,” Felix Frankfurter wrote 60 years ago, “that punishment should be meted out for conduct which at the time of its commission was not forbidden to the understanding of those who wished to observe the law.”

Which brings us to back to Black. Central to the government’s case against him is that he received compensation from his company, Hollinger International, and then re-characterized that compensation as a payment for entering into a non-competition agreement. The reason Black sought to re-characterize the payment is that under the law of Canada, where Black paid taxes, monies received from entering into a non-competition agreement are taxed at a lower rate than other forms of compensation. According to expert testimony at Black’s trial, Canada permits such a re-characterization so long as the individual claiming the lower tax rate enters into a valid, that is, enforceable, non-competition agreement — which is exactly what Black did.

Nor was there any attempt to conceal from authorities the documents and correspondence relevant to the non-competition agreement. Though Black was charged with obstruction, the basis for that charge was the removal of personal and corporate files from Black’s office after investigators had thoroughly examined and copied the files and after Black had been notified that he was being evicted from his office and consequently would be required to relocate elsewhere. The so-called obstruction occurred in the middle of the day, took place in front of security cameras, and was conducted by Black himself.

While the government disputed Black’s entitlement to the money he received, it ultimately made no difference: the federal district court, adopting the broadest possible interpretation of the honest services fraud statute, allowed the jury to convict Black without finding that Black’s alleged breach of fiduciary duty had caused Hollinger International to suffer any loss of money or property or that he even intended such harm. Nor did the court require the jury to find that Black’s actions violated any state statute or the law of Canada. As long as Black re-characterized the payments, albeit permitted under Canadian law, he was guilty of a federal crime. The unfairness of this is manifest.

What Conrad Black’s conviction demonstrates is that after 20 years of struggling, the federal courts are incapable of ridding the honest services fraud statute of its fundamental indefiniteness and the resulting iniquity of its application. For this reason, the federal court of appeals should use the opportunity of Black’s case to strike the statute as unconstitutional, thereby achieving what now is overdue.

Mr. Rips is a former clerk to Associate Justice Brennan of the U.S. Supreme Court.