WASHINGTON -- The Supreme Court on Monday made it tougher for investors to join together to sue corporations for securities fraud, a decision that could curb the number of multimillion-dollar legal settlements companies pay out each year.

But the unanimous ruling was only a modest step. It stopped short of tossing out a quarter-century-old legal theory, which might have ended securities class-action lawsuits altogether. Only three of the nine justices said they would have gone that far.

Writing for the court, Chief Justice John Roberts said companies should have a chance in the early stages of a lawsuit to show that any alleged fraud was not responsible for a drop in the company's stock price.

The change could make it more expensive and time consuming for plaintiffs at the early stages of litigation. That gives corporations a better chance to mount a defense and could discourage lawyers from bringing weaker securities cases.

The ruling is a partial victory for Halliburton Co., which is trying to block a class-action lawsuit claiming that the energy services company inflated its stock price. A group of investors claims they lost money when Halliburton's stock price dropped after revelations the company misrepresented revenues, understated its liability in asbestos litigation and overstated the benefits of a merger.

Halliburton attorney Aaron Streett said he was pleased "that the Supreme Court restored a measure of rationality and balance to securities class actions." The case now goes back to the lower courts, where Halliburton will have another chance to block the investors from joining together as a class.

The decision is a minor win for business groups that complain the growth of such class actions is a drain on corporate profits and a windfall for plaintiff lawyers. Investor groups say the lawsuits help deter corporate fraud and abuse.

But the justices rejected Halliburton's broader request to overturn the court's 1988 decision in Basic v. Levinson, a case that sparked a surge in securities class-action lawsuits against publicly traded companies and has led to an estimated $73 billion in settlements since 1997.

Under Basic's "fraud on the market" theory, shareholders who claim fraud don't need to show they actually relied on specific false statements. The theory presumes a company's false statements inflated its stock price.

Roberts said Halliburton offered no "special justification" for overruling Basic's fraud-on-the-market presumption. He said even the biggest critics of the theory "acknowledge that public information generally affects stock prices."

"Halliburton has not identified the kind of fundamental shift in economic theory that could justify overruling a precedent on the ground that it misunderstood, or has since been overtaken by, economic realities," Roberts said.

While the court's judgment was unanimous, Justice Clarence Thomas wrote a separate opinion saying that Basic should be overruled because economic realities have "undermined the foundation of the Basic premise." He was joined by Justices Antonin Scalia and Samuel Alito.

"The court's rather superficial analysis does not withstand scrutiny," Thomas said. "It cannot be seriously disputed that a great many investors do not buy or sell stock based on a belief that the stock's price accurately reflects its value."

In other Supreme Court business, the justices turned down Wisconsin's bid to begin enforcing a state law requiring abortion providers to have admitting privileges at nearby hospitals while a legal fight over the law plays out in lower federal courts.

A federal judge is weighing a challenge to the law from Parent Parenthood and others which claim that it would amount to restricting access to abortions in Wisconsin because of the difficulties doctors would face in getting the hospital privileges.

The justices did not comment Monday in declining to get involved in the case.

Also Monday, the Supreme Court left in place a ban on sports gambling in New Jersey, rebuffing an attempt to bring betting on professional and college sporting events to Atlantic City casinos and the state's racetracks.

The justices did not comment in letting stand lower court rulings that struck down New Jersey's sports betting law because it conflicts with a federal law that allows state-sanctioned sports gambling only in Nevada and three other states.

The state's appeal was led by Gov. Chris Christie. Asked for his reaction at a charity softball game at Yankee Stadium in which he was participating, Christie said the appeal was always a long-shot.

"So you know, that's the way it goes," he said. "Nothing more I can say. They said 'no' so we have to move on."

Information for this article was contributed by Wayne Parry, Jill Colvin, Geoff Mulvihill and staff members of The Associated Press.

A Section on 06/24/2014