With a unanimous 9-0 vote, the U.S. Supreme Court this week gave a welcome victory to certain private mail couriers.

The justices ruled that postal workers cannot challenge a U.S. Postal Service decision to allow competition for international deliveries. The ruling benefits private carriers who pick up mail in the United States and deliver it to post offices abroad.Postal worker unions filed suit in 1987 seeking to block a postal service regulation that gave unrestricted international mailing privileges to private companies. Such firms offered lower rates than the postal service.

The unions based their challenge on a law that requires the U.S. Postal Service to act in the public interest. They argued that the exemption for international carriers would cost the postal service $100 million a year in revenues, would result in loss of postal jobs and would benefit private business. Why benefiting private business should be considered illegal is hard to understand.

The Supreme Court justices correctly pointed out that Congress gave the postal service control over mail delivery to protect the public, not to secure postal employees' jobs. If the postal service wants to make exceptions to its monopoly, it can do so, since the law allows a suspension of the monopoly "where the public interest requires."

As of now, private firms can compete with the postal service in handling any packages, "extremely urgent" letters, and the overseas transfer of bulk mail.

While the Supreme Court verdict was limited in scope, it does further secure the role of private companies in mail delivery. As this page and others have suggested in the past, the nation might be even better served if the entire mail delivery system were thrown open to private competition.

The Supreme Court decision doesn't allow that, but it does remove some potential roadblocks in the way of such a development.