Opponents of a so-called "millionaire tax" are banking on the state's highest court to stop the issue from going before Massachusetts voters in November.
The Supreme Judicial Court is scheduled on Tuesday to hear arguments on the legal challenge which, if successful, would likely derail supporters' hopes of raising nearly $2 billion for improvements in public education and transportation.
The constitutional amendment would impose a surtax of 4 percent on any portion of an individual's annual income that exceeds $1 million.
The justices are not being asked to decide on the merits of the proposal, but instead whether it runs afoul of restrictions the state constitution places on the scope of ballot initiatives.
"It is not about whether creating a new graduated income tax is good public policy or bad public policy," said Christopher Anderson, president of the Massachusetts High Technology Council.
The Massachusetts Taxpayers Foundation, Associated Industries of Massachusetts, the Massachusetts Competitive Partnership and the state chapter of National Federation of Independent Business also joined in the suit challenging Democratic Attorney General Maura Healey's 2015 ruling that certified the initiative petition.
Raise Up Massachusetts, a coalition of community groups and unions that collected more than 150,000 signatures in support of what it calls the Fair Share Amendment, said it was confident the lawsuit will fail.
Central to the debate is Article 48 of the constitution, which among other things prohibits ballot questions from making specific state appropriations, or from combining unrelated topics into a single question.
Earmarking revenues from the tax specifically for education and transportation handcuffs legislative discretion on how to spend tax dollars, the lawsuit contends.
"Allowing this initiative on the ballot would undermine the Legislature's authority with respect to spending and taxes in one fell swoop, setting the stage of public finances to be determined not in the deliberative legislative process, but in the free-for-all of special interest-fueled initiative petitions," the business groups argued in a brief filed with the SJC.
But while the proposal does state that proceeds from the 4 percent surcharge should go "only" toward education and transportation, it also adds "subject to appropriation," three key words that would appear to give legislators at least some flexibility on how to spend any future money.
"Because that direction is expressly subject to legislative appropriation, the proposed amendment would not remove the decision how to spend the surtax revenue from the discretion of the Legislature," Healey and Secretary of State William Galvin argued in a separate brief to the court.
The state officials and supporters of the millionaire tax also dispute the plaintiffs' contention that the tax, and the funding for education and transportation, amount to unrelated provisions.
"To the contrary, no petition this simple and straightforward has ever been rejected on relatedness grounds," argues a brief filed by the 10 citizens who filed the original petition.
Some voters might want to tax millionaires but spend the money on other priorities, while others might support increased spending on education and transportation, but not the tax, the business groups contend.
Marc Perlin, a professor at Suffolk University Law School, said it was impossible to predict how the high court might come down. But as the ballot question would involve a change in the constitution -- a far lengthier and more arduous task than simply changing a state law -- he expects the justices to pay particularly close attention to the arguments.
"Amending the constitution is a momentous event," said Perlin.