The fight over a constitutional amendment that would ban same-sex marriage in Minnesota is on pace to set a fundraising record in the state, with more than $10 million raised so far by the two sides.

As the biggest push comes in the six weeks before Election Day, the marriage amendment battle could be the most expensive constitutional ballot question in state history.

"I don't believe there's been anything of this scale before," said Gary Goldsmith, executive director of the Minnesota Campaign Finance and Public Disclosure Board.

The lead group opposing the amendment, Minnesotans United for All Families, has raised money at a blistering pace -- $2.5 million since July, $5.96 million this year and more than $8.2 million since it started in 2011.

The chief group supporting the amendment, Minnesota for Marriage, raised $478,000 since July, $1.19 million this year and about $2 million overall.

But opponents' more than 4-to-1 fundraising advantage has yet to translate into surefire support at the polls. A Star Tribune Minnesota poll earlier this week found Minnesotans remain closely divided on the issue, with slightly more favoring the amendment than opposing it.

"It's really no surprise that we're being outspent," said Autumn Leva, spokeswoman for Minnesota for Marriage. "Money doesn't speak on this issue. The voices of the majority of Minnesotans are going to be heard much more loudly at the polls."

Kate Brickman, spokesman for Minnesotans United, said amendment opponents have always known they would need more than money.

"Raising money alone is not going to win us the campaign," Brickman said. "Our fundraising has been a way to get engaged in the campaign."

Business leaders split

The marriage amendment has not only divided the state's citizens, but also has business leaders taking sides.

Former Minnesota Wild hockey team owner Bob Naegele donated $25,000 to support the marriage amendment, while Mary Feltl of Minnetonka-based Feltl and Co. has given $100,000 to the cause.

The CEOs of Cargill and General Mills each donated $10,000 to Minnesotans United to oppose the amendment. Members of some of the state's wealthiest families, such as the Pohlads, who own the Minnesota Twins, and the Daytons and Carlsons also have made five- and six-figure donations to the campaign.

More than 70 percent of Minnesota for Marriage's funds come from two organizations. The Minnesota Catholic Conference Marriage Defense Fund donated $600,000 and the Minnesota Family Council Marriage Protection Fund gave $250,000.

Minnesotans United has drawn its contributions from more than 44,000 donors, with about 90 percent coming from within the state. The group's latest fundraising report does not include more than $350,000 the group raised over the weekend at hundreds of house party fundraisers.

Groups supporting same sex marriage bans have been outspent in most of the 30 states where the issue reached the ballot, but have yet to lose an election.

And, with less than six weeks until voters head to the polls, the fundraising gap between opponents and supporters is less daunting: Minnesotans United has $751,000 socked away for the election stretch run, while Minnesota for Marriage has $483,000 banked.

The total fundraising has topped totals for the 2008 Legacy Amendment vote, which until now was the largest on record, Goldsmith said.

Voter ID

The constitutional amendment that would require Minnesotans to present photo identification before they can vote has attracted about $585,000 in cash donations.

Our Vote Our Future, the main group trying to defeat the amendment, has raised $355,300 and has more than $250,000 banked for the election stretch run.

Most of the organization's support, whether via cash or in-kind contributions, has come from four sources -- church coalition ISAIAH, the Minnesota AFL-CIO, The Take Action Political Fund and Alida Messenger, a wealthy DFL activist and former wife of Gov. Mark Dayton. Messenger donated $75,000., the lead group supporting the amendment, has raised $230,600 and has $33,100 socked away.

Its biggest donor so far has been Joan Cummins, who contributed $150,000 this year. She is the wife of businessman Robert Cummins, who has donated millions to Republican candidates dating to the 1990s.

Legislative races

Individual candidates and political parties are not required to file their next pre-election campaign finance reports until Oct. 29.

But outside political groups that want to influence the outcome of races and ballot issues are reporting fundraising totals that could sway the elections.

"They're still an important source of money for candidates and party units," Goldsmith said.

Democrat-friendly groups such as WIN Minnesota and the 2012 Fund, which is backed by Messinger and many of the state's largest unions, have more than $1 million combined at their disposal between now and Election Day to help Democrats try to wrest control of the state Legislature back from Republicans.

Among the state's more prominent Republican-leaning groups, the Minnesota Chamber of Commerce's political committee, Pro Jobs Majority and the Freedom Club -- which donates exclusively to conservative candidates -- have more than $560,000 combined.

The money from these groups and other outside organizations could come to the aid of the state's Republican Party, which has been mired in debt for much of the past year.

Corey Mitchell is a correspondent in the Star Tribune Washington Bureau. Twitter: @CMitchellStrib