The Washington Supreme Court has struck down a requirement for a two-thirds majority vote in the Legislature to pass a tax increase.

A divided high court ruled 6-3 Thursday that an initiative requiring a two-thirds vote was in conflict with the state Constitution. And that lawmakers and the people of Washington would need to pass a constitutional amendment to change from a simple majority to a supermajority.

A coalition of lawmakers and education groups sued the state over the issue, and a King County judge decided last spring that the state constitution requires only a simple majority to pass tax proposals. The Supreme Court agreed to expedite its consideration.

"This ruling is a huge win for kids and schools," said Chris Korsmo, CEO of the League of Education Voters, one of the lead plaintiffs. "Washington schools need to be fully funded in order to ensure that all kids reach their potential. This ruling, combined with the recent McCleary decision, will help ensure that our kids have all the resources they need to get an excellent education."

Most people agree the state needs about $4 billion to fulfill its constitutional promise to fully pay for basic education by 2018.

The two-thirds majority rule has been approved in a series of initiatives pushed by activist Tim Eyman. Voters most recently approved the supermajority rule last November.

The majority opinion, written by Justice Susan Owens, states that under a commonsense understanding, any bill receiving a simple majority vote will become law. No language in the provision qualifies that requirement by stating a bill needs "at least a majority vote."

They wrote that without the simple majority rule in the Constitution, the people or the Legislature could require particular bills to receive 90 percent approval rather than just a two-thirds approval, thus essentially ensuring that those types of bills would never pass.

"Such a result is antithetical to the notion of a functioning government and should be rejected as such," the justices wrote.

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Correspondent Rachel La Corte contributed to this story from Olympia.