WASHINGTON - The Supreme Court is raising doubts about Alaska’s $500-a-year limit on contributions to political candidates. The justices are ordering a lower court to take a new look at the issue.

The court says in an unsigned opinion Monday that federal judges who had rejected a challenge to the contribution cap did not take account of a 2006 high court ruling invalidating low-dollar limits on political contributions in Vermont.

The Alaska challengers argue that the state is alone in imposing such low limits even on gubernatorial candidates "who must campaign across Alaska's vast expanse and widely dispersed media markets."

Justice Ruth Bader Ginsburg wrote in a short separate opinion that Alaska’s reliance on the energy industry may make the state unusually vulnerable to political corruption and justify low limits.