Massachusetts' highest court on Monday struck down a proposed "millionaire tax" ballot question, blocking it from going before state voters in November and ending advocates' hopes for generating some $2 billion in additional revenue for education and transportation.

The Supreme Judicial Court, in a 5-2 ruling, said the initiative petition should not have been certified by Democratic Attorney General Maura Healey because it violated the "relatedness" clause of the state constitution that prohibits ballot questions from mingling unrelated subjects — in this case, taxing and spending.

The proposed constitutional amendment — referred to by its proponents as the "Fair Share Amendment," would have imposed a surtax of 4 percent on any portion of an individual's annual income that exceeds $1 million. The measure called for revenues from the tax to be earmarked for transportation and education.

Writing for the majority, Associate Justice Frank Gaziano said a voter who supported the surtax but opposed earmarking the funds for a specific purpose would be left "in the untenable position of choosing which issue to support and which must be disregarded."

The justices offered hypothetical examples of voters who might support spending on one priority but not the other, such as a subway commuter with no school-age children.

The measure had been poised to reach voters in November after receiving sufficient support from the Legislature in successive two-year sessions. But several business groups, including the Massachusetts High Technology Council and Associated Industries of Massachusetts, sued to block it.

The court's ruling was a devastating blow for Raise Up Massachusetts, a coalition of labor unions, community and religious organizations that collected more than 150,000 signatures in support of the millionaire tax.