OLYMPIA — A unanimous state Supreme Court has rejected an attempt to prevent Tim Eyman's latest anti-tax measure from appearing on the November ballot.

The high court, led by Chief Justice Gerry Alexander, ruled Friday that the challenge to Initiative 960 "is not subject to pre-election review."

The ruling comes a day after the court heard arguments from the environmental group Futurewise and the Service Employees International Union, which said the initiative illegally tries to alter the state constitution.

The initiative reasserts and broadens the requirement — imposed by voters in 1993's Initiative 601 — that the Legislature approve tax increases by a two-thirds majority.

It also adds a variety of impact statements and broader public information on all tax plans and could result in more public votes on taxes.

Eyman said he was "thrilled that the court said they're not going to take away the voters' First Amendment rights."

"Courts are not going to block people from voting. That's a good thing," he said. "All of the heightened scrutiny that this lawsuit brought about has actually been in our favor. The more people know what 960 does and doesn't do, the more likely they are to support it."

Opponents argued that Eyman's measure violates state law by trying to make constitutional changes not allowed through the initiative process.

But the court said "the question of whether the initiative ultimately will violate one of the constitutional limitations in these areas is a constitutional inquiry that we will not engage in before the voters have had their say."

The Supreme Court has previously resisted considering the constitutionality of ballot measures before an election.

Friday's ruling cited a 2005 case in which the court refused to stop a doctor-supported initiative on medical malpractice from appearing on the ballot.