The state's highest court decided Tuesday that a casino repeal measure can appear on the November ballot, touching off a ferocious referendum campaign over one of the most charged issues in a generation and jeopardizing the future of the billion-dollar industry in Massachusetts.
The long-awaited ruling by the Supreme Judicial Court instantly overshadowed the state's nearly three-year debate over where casinos should be built and reignited an argument over whether they should be allowed at all.
Over the next four months, voters can expect a barrage of slick advertising, phone calls, and tenacious door knocking on the casino question, in a relentless campaign orchestrated by experienced political operatives on each side. The clash could eclipse the sleepy gubernatorial race.
"This is going to be a multimillion-dollar campaign, no doubt about it," said Springfield political strategist Anthony Cignoli, who has closely followed the development of the state's casino industry.
For passionate casino opponents across the United States, the Massachusetts repeal referendum presents a tantalizing opportunity to defeat an industry that has steamrolled opposition for years, spreading into 39 states.
"This is a very historic ballot question," Les Bernal, director of the national anticasino group, Stop Predatory Gambling, said in a recent interview.
Support for the casino industry, once quite solid in Massachusetts, has slipped over the past year as several communities voted down proposals and the gambling commission faced accusations of bias.
A Boston Globe poll this month found that only 52 percent of likely voters favored keeping the 2011 gambling law authorizing casinos on the books, while 41 percent favored repeal. A Suffolk University poll in early June found that only 37 percent approved of casinos here.
"I think the campaign will matter a lot," said Clyde Barrow, a University of Massachusetts Dartmouth casino expert. "I don't think it's a foregone conclusion for either side."
John Ribeiro, chairman of the citizen-led repeal effort, hailed the court ruling as "the starting gun in this incredibly important campaign."
"We know Massachusetts can do better than this casino mess," said Ribeiro, head of Repeal the Casino Deal. "We're elated at the opportunity to continue sharing the truth about casinos and the harm they would bring to our communities."
For the developers pursuing casinos in Massachusetts, the ruling puts about $1.7 billion a year in projected gambling revenue in jeopardy. The companies are expected to spend heavily to save the emerging Massachusetts market.
"Our fight to protect jobs and preserve this economic development opportunity for Massachusetts begins today," said Eric Schippers, a senior vice president for Penn National Gaming, the company building the state's sole slot machine parlor, in Plainville.
MGM Resorts International, which has won the right to build an $800 million gambling resort in downtown Springfield, said the troubled city is "a comeback story in progress with hard-working people eager to grow jobs and get back to work.
"We are fully prepared to extend this message to a larger audience through a statewide campaign to educate the voters on the enormous economic benefits that would be lost to the taxpayers of the Commonwealth in a repeal," said Michael Mathis, MGM Springfield president.
And the casino industry's national trade group, the American Gaming Association, promised Tuesday to "ensure that voters have the facts about our industry, instead of tired stereotypes."
In its unanimous decision, the high court ruled that Attorney General Martha Coakley made a mistake last year when she ruled that the repeal measure was unconstitutional. Coakley had said the repeal would illegally take the implied contract rights of casino developers without compensation.
The court rejected that argument.
"We conclude that . . . the Legislature and, through initiative, the voters of Massachusetts may choose to abolish casino and slot parlor gambling and parimutuel wagering on simulcast greyhound racing, and doing so would not constitute a taking of property without compensation," the court said in a lengthy decision written by Justice Ralph D. Gants.
The court also said casino developers who paid the state's $400,000 application fee and then spent millions more developing their bids had entered the process with eyes open.
"The possibility of abolition is one of the many foreseeable risks that casinos, slot parlors, and their investors take when they choose to apply for a license," the court said.
Governor Deval Patrick, who was an early champion of expanded gambling in Massachusetts and signed the casino law, said he is not surprised that one of his signature initiatives would be put to a vote.
"It is what it is," said Patrick, who said he would vote to keep the law on the books even though he has previously stated he would not support a casino in the Western Massachusetts town where he owns a home. "I think [the law is] a great balance between how we expand gaming and how we let our local communities make decisions that are right for them."
The only remaining formality facing opponents is for Secretary of State William Galvin's office to certify at least 11,485 signatures from the roughly 27,000 signatures they submitted. Opponents are confident they will meet that threshhold.
Despite the "atmosphere of uncertainty" created by the court decision, the Massachusetts Gaming Commission intends to continue its work of reviewing casino proposals, said Stephen Crosby, the commission's chairman. The panel is preparing to award the Boston area resort casino license later this summer, to either a Mohegan Sun casino proposal in Revere or a Wynn Resorts proposal in Everett.
Mayor Martin J. Walsh, who has tussled with the gambling commission in an effort to win more power over the two Boston-area projects, said he was pleased the court had "given the people of East Boston and Charlestown the right to vote, which the Massachusetts Gaming Commission has failed to do."
Anticipating the ruling, the Repeal the Deal group has in recent weeks begun to transform itself into a political campaign. The group has hired a campaign manager and an experienced fund-raiser.
Opponents will seek to knit together a number of anticasino citizens' groups that cropped up in 2012 and 2013 to fight individual casino proposals across the state. The anticasino coalition will also probably include religious leaders and public officials who actively oppose the industry.
"The challenge is to turn the grass-roots network into a unified statewide effort," said Nathan Bech, leader of a group that defeated a casino proposal in West Springfield.
On the other side, the procasino effort will include municipal officials who have embraced the industry for the jobs and revenue it promises to provide. These include Mayor Domenic Sarno of Springfield, Mayor Dan Rizzo of Revere, and Mayor Carlo DeMaria of Everett. The coalition will likely also include potential employees of the industry and labor unions eager for the construction jobs.
"Going forward, we will proceed like we did last year before our local referendum and present the facts on what this means to not only Springfield but to Western Massachusetts and the entire Commonwealth," said Sarno.
Racing fans complained Tuesday that repeal would kill the state's last harness track, Plainridge Racecourse, where Penn is building the slot parlor.
Patrick Pelosi spends several days a week at Plainridge, making small bets on horses. Without the coming slots, he said, the complex would be "dead as a doornail."
"If other states can have them, why can't we?" he said of casinos.
But Daralyn Reardon, a bartender at Suffolk Downs who supports the Mohegan Sun project, saw the benefit of a public vote. "I mean everybody has a right to vote, and this will make a final resolution . . . It's just the way it has to be," she said.
Boston University journalism professor Fred Bayles, who studies referendums, said the procasino side begins with the advantage that most voters do not live in the handful of municipalities where casinos are planned.
"The direct impact is limited to a couple of communities that have already voted in favor of it," Bayles said.
As always, money will play a large role in the campaign, and casino backers probably will outspend opponents. But in this case money alone may not guarantee a victory.
"Gaming referenda are one of the few things where the amount you spend is not necessarily the determining factor in who wins," said Barrow. "I don't think this is the kind of referendum where the gaming industry can just win it with money. They have to build a grass-roots coalition."
Cignoli, the Springfield strategist, said opponents also have more ammunition for a campaign than they did three years ago, when state lawmakers and Patrick legalized Las Vegas-style casino gambling and created a five-member commission to regulate it.
“Even the governor who put the idea of casinos forward has since said he would not want one in his town,” Cignoli said. “I do see energy on the part of the opponents.”
Peter Schworm, Claire McNeill, Priyanka Dayal McCluskey and Steven Rosenberg contributed to this story. Mark Arsenault can be reached at Mark.Arsenault@globe.com.