When Justice John Paul Stevens asked whether "reliance" was required for a violation of S.E.C. Rule 10b-5 as well as a requirement for proceeding with a private lawsuit, Shapiro exclaimed, "Excellent question!" Reliance is not part of the rule, he said, but the Central Bank ruling said it was required in private lawsuits because "[Congress] didn't want the trial lawyers to bring actions that always result in settlement."

The case has been called the business community's Roe v. Wade, attracting 30 amicus briefs. A host of business groups, including the U.S. Chamber of Commerce, the New York Stock Exchange, and Nasdaq have warned that blessing "scheme liability" would create billions of dollars in potential claims and put the U.S. at a disadvantage in the global marketplace.

Investors' advocates, among them more than 30 state attorneys general and several state pension funds, believe flagrant frauds will go unpunished if Stoneridge loses.

Patrick Coughlin of Coughlin Stoia Geller Rudman & Robbins, which represents the Enron investors, attended the arguments and came away “encouraged that [the justices] had tough questions for the other side.” Coughlin said Kennedy, who wrote the Central Bank decision, "is the key" to Stoneridge and the broader debate. He said Kennedy seemed open to Ginsburg's suggestion of a middle ground, which would be the best hope for the investors.

The S.E.C. has endorsed this test, which would hold third parties accountable if their actions had the "purpose and effect" of furthering the fraud.

But others in Bush administration, including the president himself, overruled the regulator and pushed to support the companies.