Last February, when Chief Justice John Roberts and Justice Samuel Alito of the U.S. Supreme Court sided with the court’s liberal wing in Amgen v. Connecticut Retirement Plans, they joined an opinion that left intact the standard for certification of a class of securities fraud plaintiffs. Amgen, as you probably recall, had asked the court to impose a requirement that shareholders prove the materiality of supposed corporate misrepresentations in order to win class certification. The majority refused, in a decision written by Justice Ruth Ginsburg. Among other things, Justice Ginsburg said that if Congress had wanted to tinker with the Supreme Court’s 1988 precedent on securities class certification, Basic v. Levinson, it could have done so in 1995, when lawmakers passed the Private Securities Litigation Reform Act, or again in 1998, when the Securities Litigation Uniform Standards Act became law. Instead, Justice Ginsburg wrote in Amgen, “Congress rejected calls to undo the fraud-on-the-market presumption of classwide reliance endorsed in Basic.”

But is that really what Congress did in 1995? The answer to that question could have a big impact on the future of securities class actions.

The Amgen case, as you know, led directly to this term’s securities blockbuster: Halliburton v. Erica P. John Fund, which puts Basic’s presumption of shareholder reliance on supposed corporate misstatements – and thus the foundation of most securities fraud class actions – directly before the justices. Halliburton’s lawyers at Baker Botts filed their merits brief last week, urging the court to undo Basic as bad law based on misguided economic theory. On Monday, Halliburton’s amici joined in. They’re mostly the usual suspects: the U.S. Chamber of Commerce and other pro-business organizations; the Securities Industry and Financial Markets Association; the American Institute of Certified Public Accountants; the Washington Legal Foundation; and DRI – The Voice of the Defense Bar. Two different groups of law professors filed briefs, one a technical argument about the efficient-market theory underlying Basic and the other a scholarly condemnation of securities class action litigation.

I was particularly intrigued, though, by a brief that purports to support neither side, filed by five former Republican members of Congress and seven former Congressional and Securities and Exchange Commission staffers, all of whom were involved in the passage of securities litigation reform in 1995. (The SEC staffers served under Democrat-appointed SEC chairman Arthur Levitt.) According to this brief, Justice Ginsburg wasn’t quite right when she concluded in Amgen that Congress rejected calls to do away with Basic. The 1995 law passed by both houses, overriding a veto by President Clinton, didn’t actually end up addressing the fraud-on-the-market theory of classwide investor reliance at all – which, according to the brief, should not be construed by the Supreme Court as a rejection of efforts to repudiate the precedent.

“Congress did not answer any of the competing calls to overturn, modify, or codify the Basic presumption,” Sullivan & Cromwell argued for the amici. “Congress was simply silent in response to those various requests, and this court should not take Congress’s silence as implicit acceptance or rejection of Basic’s fraud-on-the-market theory.”