The Supreme Court is making it tougher for investors to join together to sue corporations for securities fraud.

The justices said Monday that companies should have a chance at 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 ruling is a partial victory for Halliburton Co., which is trying to block a class-action lawsuit claiming the energy services company inflated its stock price.

It is also a modest win for business groups that hoped to make it more difficult for plaintiffs to bring class-action cases.

But the high court rejected Halliburton's request to overturn a quarter-century-old precedent that has made it easier for plaintiffs to negotiate billions of dollars in legal settlements.