Millions of dollars are already flowing into the campaigns behind five referendum questions headed to Maine voters this November, potentially setting the stage for record-setting spending on ballot initiatives in the state.

The campaign to expand background checks on private gun sales – one of five citizen’s initiatives on Maine’s November ballot – received more than $2.1 million in donations during May alone, including a $1.7 million contribution on May 26 from the gun-control group backed by former New York City Mayor Michael Bloomberg. Factoring money raised and spent to collect petition signatures to qualify for the ballot, the campaign has received roughly $3 million overall, much of that from Bloomberg’s Everytown for Gun Safety group, according to campaign finance reports filed with the state.

“We have had great support from our partners and they have provided us with early money to run statewide on an important issue,” said David Farmer, campaign manager for Mainers for Responsible Gun Ownership, which wants to require federal background checks on most private, person-to-person gun sales. “We know the gun lobby has millions of dollars at their disposal … It’s expensive to run elections and we are going to be raising money both in-state and from our national partners.”

The NRA’s Institute for Legislative Action had only spent about $31,000 in Maine as of May 31, including $28,600 on polling, according to documents filed with the Maine Commission on Governmental Ethics and Election Practices. But the NRA and other gun owners’ rights groups, including the Sportsman’s Alliance of Maine, are expected to counter with their own aggressive campaigns against a Maine proposal they believe is unnecessary and will only lead to burdensome restrictions on law-abiding gun owners.

“New York City billionaire Michael Bloomberg is single-handedly bankrolling the Maine gun-control ballot initiative in order to push his big-city-style anti-gun agenda on law-abiding gun owners in the Pine Tree State,” Lars Dalseide, spokesman for the NRA Institute for Legislative Action, said in a statement. “Despite the gun-control lobby’s misleading rhetoric, Bloomberg’s initiative will not reduce crime and instead will place excessive restrictions on law-abiding citizens, turning them into criminals. We cannot let Bloomberg’s Wall Street fortune drown out the voices of Second Amendment supporters in Maine.”

Costly ballot initiative campaigns are not a new phenomenon in Maine. In 2009, supporters of same-sex marriage spent more than $4.5 million in their unsuccessful campaign to legalize the practice in Maine. Opponents of bear hunting using bait, traps and dogs spent $2.5 million on their failed campaign to ban the practices in 2014.

But the 2016 election season is shaping up to be the costliest in Maine history, at least for ballot initiatives. The five citizen’s initiatives on the ballot this November represent a record for Maine.

In addition to gun background checks, Maine voters will also be asked whether they want to: legalize marijuana for recreational use; increase the state’s minimum wage to $12 an hour by 2020; impose a 3 percent surcharge on households earning $200,000 or more to increase funding to public schools; and approve a ranked-choice voting system in the state.

Many of those campaigns have also received sizable checks from outside the state.

Mainers for Fair Wages, the ballot question committee organized by the Maine People’s Alliance and the Maine AFL-CIO to increase Maine’s minimum wage to $12 an hour by 2020, had received $152,250 in donations this year through May 31. The California-based Stephen M. Silberstein Foundation, which supports progressive causes, gave $50,000 to the campaign while the Restaurant Opportunities Centers United in New York donated $25,000. Another California-based group that supports higher minimum wages, The Fairness Project, has also set up a political action committee in Maine with $40,000 in the bank so far.

The effort to legalize marijuana for recreational use, meanwhile, received $245,000 in contributions between Jan. 1 and May 31, in addition to more than $450,000 collected last year by the campaign and its now-partner Legalize Maine during the signature-gathering process.

Among the campaign’s largest donations to date this year are $100,000 from the New Approach PAC based in Washington, D.C., $25,000 from Drug Policy Action in New York and $25,000 from the Marijuana Policy Project, the national group helping lead legalization measures in Maine and other states.

Legalization referendum questions could be on ballots in more than a half-dozen states this fall if all of those currently in the works qualify for their respective ballots. But David Boyer with the Campaign to Regulate Marijuana Like Alcohol, the group organizing Maine’s legalization ballot initiative, said organizations around the country are watching to see whether Maine and Massachusetts become the first East Coast states to legalize the drug. And that prospect could translate into donations.

“There is a lot going on this year,” Boyer said. “California, Nevada, Arizona are all looking at regulating marijuana like alcohol. And California is a big state, so there is a lot of attention there. Maine is a small state … but our grassroots (movement) in Maine has always been looked at as a leader” on marijuana issues.

Citizens who Support Maine’s Public Schools, the political action committee formed by the Maine Education Association, had received $105,000 through May 31 from the MEA in support of the K-12 funding ballot initiative. The referendum would impose a 3 percent “surcharge” on household income above $200,000 to help finance public education.

The Committee for Ranked Choice Voting received the bulk of its $71,000 in donations through May 31 from individual donors. Another political action committee supporting the ballot initiative, called The Chamberlain Project PAC, has received $50,000 from the Action Now Initiative based in Texas.

However, perhaps the biggest-money campaign in Maine this election cycle didn’t even qualify for the November ballot.

Horseracing Jobs Fairness spent roughly $3.2 million from late 2015 through May 31 attempting to secure a place on the ballot for a referendum seeking voter approval for another casino in southern Maine. All of that money came from one person, Lisa Scott of Florida. She is the sister of international casino developer Shawn Scott, who led the 2003 referendum campaign that authorized Maine’s first combination horse racetrack/slots casino in Bangor.

The Maine Secretary of State’s Office said the campaign failed to qualify for the ballot because Secretary of State Matt Dunlap invalidated tens of thousands of signatures gathered by the paid workers.