AUGUSTA — The group backing a statewide ballot effort to require background checks for private gun sales has received a large donation from an out-of-state donor, according to the latest campaign finance reports released this week.

The $125,000 donation from Seattle-based entrepreneur Nicolas Hanauer to the Mainers for Responsible Gun Ownership brought the campaign’s total contributions to more than $2.3 million. The group also received $25,000 from Maine author Stephen King, according to the report from the period ending July 19.

As of Tuesday, opponents of the background checks raised just over $40,000, most of it donated by the National Rifle Association.

Of the five referendum questions going to Maine voters in November, the gun control question has by far attracted the most contributions, finance reports show.

The pro-background checks group had $432,886 on hand at the end of the reporting period, having already spent heavily on TV advertising to run this fall, as well as consultants, polling and staff. The National Rifle Association’s Institute for Legislative Action was reporting $335 cash on hand.

The Seattle-based donor, Hanauer, is a businessman and venture capitalist who was one of the first investors in Web retail giant Amazon. Hanauer was also among a trio of billionaires, including Bill Gates and Steve Ballmer, who helped bankroll a similar ballot question in Washington state that was approved in 2014. In the Washington campaign, background check supporters raised more than $10 million compared to the NRA-backed opponent campaign’s $600,000.

Hanauer also backs raising the federal minimum wage to $15 an hour.

Other significant donors listed in previous campaign finance reports include a group backed by former New York City Mayor Michael Bloomberg’s Everytown for Gun Safety Action Fund, which donated $1.7 million in May.

The campaign also has collected small donations of $100 to $500 from Maine residents. Among them is former Lewiston Mayor Larry Gilbert Sr., who donated $100, retired U.S. Attorney for the District of Maine Paula Silsby, who gave $500, and outgoing state Senate Minority Leader Justin Alfond, D-Portland, who gave $250.

The latest finance report was filed this week with the Maine Commission on Governmental Ethics and Election Practices.

The background check question – “Do you want to change Maine law to require background checks prior to the transfer of firearms between individuals, with some exceptions for certain circumstances?” – will appear third of the five on the state ballot in November.

Other ballot questions would ask voters whether they want to legalize marijuana for recreational use, increase the minimum wage to $12 an hour by 2020, establish a ranked-choice voting system and create a new 3 percent tax on annual incomes over $200,000 to create a new fund for public education.

Marijuana legalization proponents had the second most cash on hand with just under $93,000 as of Tuesday. To date, the Campaign to Regulate Marijuana Like Alcohol has collected $436,285 in donations, with the bulk coming from a Washington-D.C.-based political action committee, New Approach.

While background-check supporters have received the most donations, the effort also has a high-profile opponent in Gov. Paul LePage, who also opposes the minimum wage increase question.

LePage took aim at the background check effort during a town hall forum in Paris on Wednesday night, saying it would violate the Declaration of Rights in the Maine Constitution. The declaration states, “Every citizen has a right to keep and bear arms and this right shall never be questioned.”

“That one is unconstitutional,” LePage said. He also told the audience that the ballot effort’s goal is to create a gun registry in Maine.

David Farmer, the campaign’s manager, said LePage was misleading people.

“The governor is just wrong on this and has been,” Farmer said Thursday. Farmer cited U.S. Supreme Court case law that provides precedent for placing reasonable limits on constitutional rights, including gun ownership.

Farmer also said that those who have criticized the campaign for being fueled with out-of-state cash have overlooked the hundreds of Maine donors to the campaign and the 85,000 Maine voters who signed petitions to put the question on the ballot.

A Maine background check for private gun sales would be the same as those required for gun sales by federally licensed firearms dealers Farmer said. He added that creating a gun registry would also be prohibited under federal law.