VOTERS WILL NOT have a $5 billion question to answer after all.

The state’s highest court on Thursday tossed a measure seeking to trim the income tax rate by one-fifth from the November ballot, stopping in its tracks a bruising, months-long political fight that would have carried major implications for both household budgets and public services.

Justices on the Supreme Judicial Court ruled that the attorney general’s office erred in its summary of the question, rendering the measure ineligible to appear before voters in November.

It’s a massive decision that cuts the fuse of a revenue bomb that had top Democrats in the House, Senate, and corner office sweating. Independent analysts estimated that reducing the income tax rate from 5 percent to 4 percent, once fully implemented, would trim more than $5 billion from the state’s coffers, likely forcing cuts to public spending.

Justice Serge Georges, Jr., writing for a unanimous court, said the official summary produced by Attorney General Andrea Campbell’s team “misstates the petition’s impact” by incorrectly stating the rate cut would not impact taxes on long-term capital gains.

“The summary’s contrary statement is not a minor imprecision. It is significantly misleading and likely to influence voters,” Georges wrote, concluding that the AG’s office therefore did not provide a sufficiently “fair” summary.

A business-backed coalition led by the Massachusetts High Technology Council, the Pioneer Institute, and the Massachusetts Competitive Partnership pitched the question as a way to relieve residents from the state’s high cost of living and stem the long-running flow of outmigration.

The coalition is also behind a separate ballot question that would overhaul a tax-cap law, often known as Chapter 62F, to make it much more likely that Beacon Hill needs to refund money to taxpayers at the end of each budget cycle. That measure did not face a legal challenge and remains on track to be decided by voters this fall.

Colin Reed, a spokesman for one of the proponent groups, the Massachusetts Opportunity Alliance, called the decision an “unprecedented ruling” that “prevents Massachusetts voters from weighing in on a popular proposal to address the state’s cost-of-living crisis.”

“It does not change the underlying reality: Massachusetts remains one of the most expensive states in the nation, with too many residents leaving in search of greater opportunity and a lower cost of living,” Reed said in a statement. “Today’s court decision does not eliminate the urgent need for action.”

Jim Stergios, executive director of the Pioneer Institute, lamented that an error by the attorney general’s office, not the campaign itself, proved fatal.

“The larger issue is whether voters should lose the opportunity to decide an important economic question because of a drafting error in a government-prepared summary,” Stergios said in a statement. “No ballot question has ever been removed due to a minor drafting mistake. Today’s decision means that a technical defect in a summary prepared by the government can prevent voters from considering a question that otherwise qualified for the ballot.”

Labor groups who opposed the measure — and who four years ago led the successful charge to impose a surtax on wealthy households, to the chagrin of some business groups like the Massachusetts High Technology Council — cheered the decision.

“This tax cut campaign was never about delivering real relief for working class families facing an affordability crisis,” said Harris Gruman, chair of the opposition campaign and executive director of the SEIU Massachusetts State Council. “Even the income tax cut they proposed was about sneaking through a tax break for ultra-rich investors. And their true goal all along was to leverage the initiative into a deal to secure more tax breaks for ultra-rich investors and wealthy heirs, along with massive giveaways to profitable corporations.”

The benefits from the question would be far more significant for high-earning taxpayers. Households with incomes between $75,000 and $200,000 would receive an average tax cut of $1,267, while those that make more than $1 million would get an average cut of $37,421, according to the Center for State Policy Analysis at Tufts University, which neither supported nor opposed the measure.

Opponents, including lawmakers and the plaintiffs who brough the matter to the high court, argued that reducing state tax revenues by billions of dollars would force cuts to social services so severe they would offset the benefits for most residents except the wealthy.

For a time, nervous legislators were content to bash the ballot initiative while holding out hope that the SJC would take the matter off their plates.

Lawmakers will no longer face pressure to negotiate with proponents on more modest tax cut alternatives to the ballot question, and top Democrats get to avoid spending the coming months campaigning against lowering taxes, achieving the outcome they want while keeping their hands more or less clean. Plus, the potentially record field of ballot initiatives — many of which are united by an undercurrent of frustration with legislative inertia — shrinks again.

“A $5 billion annual loss in state revenue would’ve meant significant cuts to services and programs that Massachusetts residents rely on, while doing little to bolster competitiveness and address the affordability challenges facing the Commonwealth,” House Speaker Ron Mariano said in a statement. “I’m grateful that this irresponsible initiative petition won’t appear on the ballot in November.”

The decision came less than two weeks before the Secretary of State’s office needs to have certified signatures in hand to begin printing out the ballot question guide for voters.

At oral arguments before the SJC in May, Justice Scott Kafker said the summary was “bothersome to me, because my reading of that is capital gains is not included. It’s not just a material omission, in [the plaintiff’s] view, it’s a material misrepresentation.”

The court used almost that exact language in its final decision.

In a statement after the ruling, a spokesperson for the AG’s office said, “we respect the SJC’s decision and will continue to work diligently to ensure that ballot initiatives are summarized fairly and transparently.”

There seemed to be little dispute before the high court that the written description was inaccurate, though the measure’s proponents argued that the attorney general is not required to describe every downstream effect of a ballot measure in its summary.

One option — to force a correction to the summary and have the campaign collect the tens of thousands of signatures all over again — was dispensed with quickly by justices. Constitutionally set timeframes for submitting the bulk of signatures had already passed, they noted.

Those fighting the measure, and even the attorney general’s office defending its work, agreed that the entire thing should be struck from the ballot if the summary is “so unfair to the voters,” as the AG’s office put it.

“Allowing a new summary at this stage would create a different constitutional sequence from the one [the state Constitution] prescribes,” Georges wrote. “It would also call into question the validity of the more than 85,000 signatures already gathered on forms bearing the unfair summary.”

Not all legal minds agreed that this was the best course of action. Robert Cordy, a retired associate justice of the SJC, wrote in an op-ed for CommonWealth Beacon that the high court should keep the question on the ballot.

“Removing the initiative from the ballot just because critics object to the phrasing of a summary could undermine public confidence in the initiative process itself,” he warned.

The high court last Friday gave the green light to a dark money-backed ballot measure seeking to roll back recreational cannabis legalization. In its decision, the unanimous SJC said the measure could proceed to the ballot despite complaints about the attorney general’s summary. The summary did not introduce a clear error and “is not the only source of information for voters,” the court wrote in that ruling.

Just six days later, the SJC declared the summary error for the income tax ballot question essentially unfixable. Campaign materials could not “cure” the error, Georges wrote, nor could the already published “yes” and “no” statements from the Secretary of State’s office describing what a vote for or against would do. The statements do not mention capital gains.

And the way voters would encounter the summary along with the actual text of the measure would make things even more confusing.

“A voter reading the petition and the summary together would see a summary that expressly excludes capital gain income and a petition that says nothing to contradict that statement,” Georges wrote.

The decision trims the field of ballot questions remaining in the mix for November from 11 to 10, which would set a record. That could change soon: The court is still weighing legal challenges to two other ballot questions, one seeking to revive rent control with a strict statewide cap, and the other to replace partisan primary elections with a single, “all-party” primary featuring every candidate regardless of party.

Those decisions are expected to arrive in the coming days.