Suffolk District Attorney Daniel Conley, a candidate for mayor, on Sunday raised questions about the legality of an East Boston-only vote on a Suffolk Downs casino. Conley added that the 13-member City Council should “come to their senses” and move to endorse a city-wide vote.

While saying he does not favor or oppose a casino, Conley argued the project would affect the entire city and 95 percent of Boston will not be able to weigh in if the vote is limited to one neighborhood. Conley has also argued that if East Boston votes to reject a casino while the rest of the city votes in favor, the neighborhood should be given the final say.

At a late afternoon press conference on City Hall Plaza, Conley said that if the entire city rejects having a casino in East Boston, he would support the decision and file a lawsuit to prevent a resort casino from locating in Everett, as gambling mogul Steve Wynn has proposed. The city of Everett has voted in favor of the Wynn project, but residents of Charlestown and Somerville will bear the burden of it without receiving benefits, he said.

Conley’s remarks took aim at several city councillors – five of them are running for mayor, with most of them on-the-record as supporting an East Boston-only vote – and singled out John Connolly, who has topped several recent polls. Outgoing Mayor Thomas Menino also supports an East Boston-only vote, saying the neighborhood should have the sign-off because it will be directly affected by the proposed casino.

“I’ve heard talk from John and most of the other candidates about having more openness and transparency in how we deal with development proposals,” Conley said. “But here we have the first real test of those words and none of them will back those words up and give our residents a voice and a vote.”

The state’s expanded gambling law allows cities with populations over 100,000 to restrict a vote to just the ward where the gambling facility would be located. “Now I believe – I’m also an attorney, as you know, I’m the district attorney – I believe that’s [a] constitutionally-flawed argument anyways,” Conley said. “So my expectation would be that if there is a referendum here in Boston, we may very well see a challenge on the constitutionality of an East Boston-only vote. For me though, it’s really is not so much a legalistic argument.”

Conley’s comments echoed those of Secretary of State Bill Galvin, the state's elections chief, who raised legal concerns about a ward-only vote during the debate over expanding the state’s gambling laws in 2011.

“As far as I’m concerned, we’re one Boston; a casino, something that large over in East Boston is going to affect everybody in our city and everybody ought to have a vote,” Conley said.

Asked if he would support a lawsuit questioning the constitutionality of a ward-only vote, Conley said, “I believe that I would in light of the fact that I believe that we ought to all have a say in the matter. But this is where I ask – this can all be averted. This can all be averted if the members of the City Council come to their senses and have a vote in the City Council to make it a citywide vote.”

Conley noted that councillors in Springfield voted earlier this year to take a casino vote citywide, when they could have limited to just the one ward.

Menino administration officials are negotiating a mitigation agreement with Suffolk Downs. On Sunday, while attending a gospel music festival on City Hall Plaza an hour after Conley’s press conference, Menino said there would be an announcement on the agreement “shortly.”

Conley’s aggressive tone comes nearly a week after another mayoral candidate, Codman Square Health Center co-founder Bill Walczak, stepped up his opposition to a casino. Walczak wrote a letter to the state’s gambling commission, citing negative social impacts as the reasons behind his resistance.

A Walczak spokeswoman attended Conley’s press conference on Sunday. Afterward, Dee Dee Edmondson, the spokeswoman, said, “The only candidate that is 100 percent against the Suffolk Downs and Everett casinos is Bill Walczak. The rest are just dancing around the issue and trying to find wiggle room in the middle ground between for and against.”

Conley’s nuanced stance has cost him the support of a state representative. Carlo Basile, an East Boston Democrat who supports keeping it a neighborhood-only vote, abandoned Conley for City Councillor At-Large Connolly after the district attorney recently said the entire city should vote on a casino, with the neighborhood getting a preference.

"I've been clear since day one that neighbors should have more input about developments in their community and the same is true here," Connolly said in a statement on Sunday. "If the casino were proposed for Hyde Park, would the people of Hyde Park want East Boston to decide?"

District Attorney Conley's statement is available below, as prepared for delivery:

I'm not from East Boston. None of the Mayoral Candidates are from East Boston. But I love what it stands for: it's a beautiful, wonderful, diverse neighborhood. It's a place where all kinds of people work hard to make a good life for their families. It's a place where people don't run away from problems, they fix them.

Of course East Boston, like any neighborhood, has its challenges - and if I'm elected Mayor, I'm going to be ready to use my experience both as a City Councilor and as a District Attorney to fix them. That's a commitment I'm making to people in neighborhoods all over this city.

But this election isn't about making commitments - anybody can make promises. This election is about leadership, and taking a stand for what’s right, regardless of the political consequences. To get where we want to go, Boston is going to need strong, proven leadership. The city is going to need consistent leadership. And from East Boston to Hyde Park and every neighborhood in between, people deserve to know where their candidates stand and why.

Given its potential costs, the proposal to locate a casino in East Boston is one of the most consequential economic decisions in the history of our city. So far, there has not been one credible argument put forward by any of the candidates arguing that the impact of the casino would end at the boundary lines of East Boston.

We all know the truth. We know that this will absolutely affect the entire city – the services we provide, our traffic and transportation systems, Boston’s hotels, restaurants, bars, entertainment venues and the tens of thousands of jobs they support, its easy accessibility to poorer communities and what that means, and, most importantly, the city’s very tax base and finances.

Even within East Boston, I’ve heard from so many residents who are concerned about the traffic impacts, crime impacts, addiction, economic costs, and their own property values. Some of them oppose a casino, some see the benefits as outweighing the costs and some are unsure, but they are all frustrated with a process that is anything but open, transparent and predictable.

We should be having a wide ranging discussion of the merits of this proposal, but so far, any debate about a casino has been stifled, shied away from or shouted down. The people of Boston and the residents of East Boston deserve better. Even after a mitigation agreement is signed, over 95 percent of the voters in Boston won’t be allowed any input.

Well I share their concerns. And any time a community is disregarded, circumvented, outspent, and out-lobbied, we all should share their concerns. Boston has a great and proud history of leadership and standing up for our ideals.

I've always been a leader who stands up for Boston's communities. And I'm going to be a candidate and a mayor who stands up for fair and open processes. So far, not only has this polarizing and divisive development process isolated and disenfranchised half the voices of East Boston, it has bypassed public debate on the citywide level, where it belongs.

Every one of us running for mayor is seeking an office where we are supposed to protect the interests of every neighborhood and the entire city. And yet not one of the elected officials seeking the office of mayor sees any contradiction with a plan to allow a project that will affect the entire city to go forward while disenfranchising most of the city.

I want to be very clear: I am neither opposing nor supporting a casino in East Boston. What I am doing is putting my faith in the people of Boston and East Boston to make up their own minds after they have had a full and fair opportunity to consider the suggested benefits and the potential risks.

As I proposed previously, I believe that the referendum should be citywide. I believe that the host neighborhood should be in a position of primacy and if it rejects a casino, even if the city as a whole accepted it, then it should be rejected. But I also believe that if the city as a whole opposes the casino then it should not happen.

John Connolly recently said that he has some supporters who are for a casino and others who are against. Other candidates have said the same. I’ve got supporters in East Boston and across the city who are on both sides of the casino question, too, but where we differ is I believe everyone deserves to be heard.

Similarly, I’ve heard a lot of talk from John and most of the other candidates about having more openness and transparency in how we deal with development proposals. But here we have the first real test of those words and none of them will back those words up and give our residents a voice and a vote.

Should the people of Boston AND East Boston both sign off in support of a casino, my job as mayor will be to ensure that it lives up to its every promise and that the potential negative effects are held to a minimum.

Conversely, should the proposal be rejected, then I will not only support the decision to keep a casino out of Boston, but I will also file suit to prevent a casino from locating in Everett.

Like the East Boston proposal, the Wynn proposal was voted on in just one community, while residents and businesses from Charlestown to Somerville and beyond will bear its traffic, economic, and social burdens but receive none of the proposed benefits. The burdens of a casino don’t stop at the lines drawn on a map. Neither should we allow those artificial lines to define the limits of a public debate that is sorely needed.