WASHINGTON — The Supreme Court on Monday made it harder for investors to band together to pursue claims that they were misled when they bought or sold securities. But the justices did not accept a broader challenge, one that could have put an end to most class actions for securities fraud.

Business groups expressed tempered enthusiasm for the decision, calling it a small step.

“While today’s decision inches toward bringing securities law back in line with the ordinary rules for proving fraud cases, much more can and should be done,” said Lily Claffee, general counsel of the United States Chamber of Commerce.

Chief Justice John G. Roberts Jr., writing for the majority in a unanimous decision that split 6 to 3 on its rationales, said that defendants facing class actions might try to show at an early stage that their statements did not affect their securities’ market price.

The decision, in a case involving the oil services company Halliburton, will cut back on suits that can involve enormous sums. Settlements involving companies and investors over the last decade have totaled about $62 billion, with about $10.5 billion of that amount going to plaintiffs’ lawyers, according to a report from NERA, an economic consulting firm.