In a unanimous ruling, the justices said the Fair Credit Reporting Act required an insurance company to notify customers it was charging higher-than-preferred rates only if the rate was based on a low credit score.
If a credit score was one of several considerations in the decision and did not by itself alter the pricing, the law did not require insurers to notify customers, the high court said.
"Though some textual arguments point another way, it makes more sense to suspect that Congress meant to require notice and prompt a consumer challenge only when the consumer would gain something if the challenge succeeded," Justice David Souter wrote in the court's opinion.
Sending out notices to "every young applicant who had yet to establish a gilt-edged credit report" would make the reports "formalities, and formalities tend to be ignored," Souter wrote.
The court said Geico General Insurance Co. did not violate the credit law by not notifying customers about how their credit scores were used in insurance pricing decisions. Safeco Insurance Co. of America "might have," but did not do so recklessly, the court said.
The insurance industry had said it would face billions of dollars in damage claims if it lost the case.