The Supreme Court on Wednesday struck down part of a federal anti-corruption law that makes it a crime for state and local officials to take gifts valued at more than $5,000 from a donor who had previously been awarded lucrative contracts or other government benefits thanks to the efforts of the official.

By a 6-3 vote, the justices overturned the conviction of a former Indiana mayor who asked for and took a $13,000 payment from the owners of a local truck dealership after he helped them win $1.1 million in city contracts for the purchase of garbage trucks.

In ruling for the former mayor, the justices drew a distinction between bribery, which requires proof of an illegal deal, and a gratuity that can be a gift or a reward for a past favor. They said the officials may be charged and prosecuted for bribery, but not for simply taking money for past favors if there was no proof of an illicit deal.