The Minnesota Supreme Court says Minneapolis can go ahead with its plans for instant runoff voting for city offices.

The justices on Thursday ruled against a group that challenged the constitutionality of the system, an alternative method in which voters rank their choices for each office instead of casting just one vote for one candidate in a race. The system eliminates the need for separate primary and general elections.

Critics say it violates the principle of one person, one vote.

But the Supreme Court says the instant runoff voting method adopted by Minneapolis does not violate the U.S. or Minnesota constitutions. The decision affirms a lower-court decision that also backed the system, which Minneapolis voters approved in 2006.