In Skilling's case, the jury found that he schemed to inflate Enron's stock price to hide the true dire financial state of the company. While the government argued that his actions caused shareholders to lose money, Skilling contends that his actions never lined his own pockets.
Srinivasan said the statute was vague enough that there was a danger it could convert "any work place lie" into a felony.
Experts say the statute has become a crucial tool for prosecutors using it against corporate executives who allegedly put their personal financial interests ahead of their duties to shareholders.
"The big complaint about honest services is that nobody knows what it means. The statute is really vaguely written, which makes it valuable to prosecutors because they can fit a lot in it," said Adam Gershowitz of the University of Houston Law School.
But the government scoffs at the notion that Skilling didn't privately gain from his actions. In its briefs, the government writes that Skilling's "deception deprived shareholders of the information they needed to make informed decisions and thereby defrauded them of his honest services."
At trial, prosecutors said Skilling and Enron founder Kenneth Lay "chose to violate their duties of loyalty and trust by lying over and over again about the true financial condition of Enron, concealing from [the] employees and investors information which was critical for them to make good decisions about what to do with their own stock; and at the same time, they repeatedly put their own interests in front of those investors by self-dealing, by selling their own stock."
Critics of the law say the government didn't need it to go against Skilling.
"Their invocation of honest services reflects an overreach on the part of the government, which could have used more established law," said Noel J. Francisco of Jones Day. "It's a vague and amorphous law."
In two other cases before the Supreme Court, justices on both sides of the ideological spectrum have expressed some reservation about the law.
Experts have said the court could wipe it off the books or give it a more narrow interpretation.
"They could say it only applies to bribery and basically conduct that is unambiguously corrupt," Francisco said.
The court will decide the case by June.