In a major blow to the national protest movement against classroom budget cuts and stagnant teachers’ salaries, the Arizona Supreme Court blocked a ballot initiative Wednesday that would have increased taxes on the wealthy to help raise money for schools.

Teachers, unions and activists have shifted their focus to the ballot box in recent months, after educators in six states walked out of their schools this year. Among their biggest targets was proudly libertarian Arizona, where proponents gathered far more signatures than the number necessary to put the tax initiative, called Invest in Education, on the ballot.

The court said, however, that the wording of the proposition could have confused voters about the extent of the proposed tax increase, in part because of questions about whether taxpayers’ income levels would be adjusted for inflation. The measure would have raised $690 million annually for education.

“This is absolutely stunning, and it denies citizens and teachers what they fought so hard for — the opportunity to fund our students and schools,” Noah Karvelis, a music teacher and one of the leaders of the Arizona walkout, said in an email. “Over 270,000 signatures were just thrown out by the court.”