A national organization emerging as a driving force in the effort to block same-sex marriage around the country is the single-largest contributor to the group trying to pass the Minnesota marriage amendment.

The National Organization for Marriage has poured $1.65 million into Minnesota for Marriage, and nearly all of that came this month, new campaign finance records show. The group gave another $225,000 on Wednesday.

All told, Minnesota for Marriage raised more than $3.7 million so far this year, much of it from the Catholic Church, affiliated groups and the National Organization for Marriage. That's still far less than the group's opponents.

John Helmberger, chairman for Minnesota for Marriage, said their side is accustomed to being dramatically outspent in marriage-related measures in other states.

"Those who want to redefine marriage may outspend us, but no matter how much they spend, we are confident that the voters will do as they have done in … other states and vote to protect marriage,” he said.

Minnesotans United for All Families, the lead group trying to defeat the measure, has raised more than $11 million in cash and in-kind support.

That group's single-largest contribution came from the Human Rights Campaign, the nation’s largest lesbian, gay, bisexual and transgender civil rights organization. The group has given Minnesotans United more than $1.1 million in cash and in-kind support.

Money continues to pour into the race.

Hollywood actor Brad Pitt gave $100,000 to the Human Rights Campaign.

The group matched the Pitt contribution and will send a $50,000 to Minnesota to help defeat the amendment.