Just months after the Supreme Court begins hearing arguments in Halliburton Co. v. Erica P. John Fund on March 5, CFOs could suddenly find that their companies have much smaller legal risks, fees and insurance costs, attorneys say.

The reason? If the nation’s highest court rules in favor of Halliburton, it could deal a coup de grâce to a prime theory that plaintiffs’ lawyers rely on to amass federal securities class-action suits against companies whose representatives have allegedly made materially false, market-moving statements to shareholders.

In the case, Halliburton Co. v. Erica P. John Fund, the Supreme Court will decide whether it should overrule or make big changes in the longstanding “fraud-on-the-market presumption.”

A relative of the “efficient markets hypothesis,” the theory enables plaintiffs to form a class without having to prove that each investor suffered financial loss resulting from a company’s misleading statements. Instead, the Supreme Court previously ruled, courts can presume that the share price set by the stock market as a whole takes into account the effects of such information.

The stakes for corporations of the court’s decision on its own 25-year-old ruling in Basic Inc.v. Levinson are high. “If Halliburton prevails, then the entire ecology of the market for class-action securities-fraud litigation is likely to undergo a dramatic change,” Joseph Grundfest, director of The Stanford Law School Securities Class Action Clearinghouse, is quoted as saying in the just-released annual review of securities class-action filings (done in cooperation with Cornerstone Research).

If the court goes along with what Halliburton is requesting, “it will really be fairly devastating for the plaintiffs’ bar in securities class actions,” says C. William Phillips, an attorney with Covington & Burling who represents companies in such cases.

In the case the Supreme Court will hear, the lead plaintiff, the Erica P. John Fund, which supports the Catholic Archdiocese of Milwaukee, contends that Halliburton, the oil-services company, misrepresented itself in three ways: its potential liability in asbestos litigation; its accounting for revenue on fixed-price construction contracts; and its potential benefits from a merger. The fund maintains that shareholders lost money when Halliburton’s stock price dropped following the release of negative news concerning the misrepresentations.

Noting that securities class actions “have been the subject of tightening and limiting by the courts and Congress” since the Private Securities Litigation Reform Act became law in 1995, Phillips said that if the Supreme Court rules with Halliburton, “you won’t have anywhere near as many” securities class actions based on misrepresentation as occur now. (In 2013, about one in 29 companies in the S&P 500 was a defendant in a class-action filed during the year, according to the Cornerstone report.)

The effects of a pro-Halliburton ruling “will be reflected not only in fewer payments to settle litigation, to lawyers to litigate, but also in the insurance premiums needed to insure against the risk,” he says.