The lead group opposing the marriage amendment raised more than $350,000 this weekend through a blitz of fundraisers.

Minnesotans United for All Families supporters hosted 307 house parties in every corner from the state, with attendance ranging from a handful of guests to hundreds. All told, 30,000 people attended the fundraisers as part of the One Day United event, according to the campaign.

This was the third time the group hosted the One Day United event. Last November, supporters hosted 100 parties. A second one in May resulted in 200 parties.

"It was pretty extraordinary to have more than 300 parties in a single day across the state," said Richard Carlbom, campaign manager for Minnesotans United. "After May's One Day United, we really wondered if it would be possible to bring this many people together, but the energy out there to defeat this thing made it possible. I don't think Minnesota has ever seen something with this much momentum behind it."

Campaigns on both sides are frantically trying to identify supporters and raise money for a campaign that is shaping up to be expensive and exceedingly close. A new Star Tribune Minnesota Poll found that supporters with a slight edge, at 49 percent to 47 percent opposed. Factoring in the margin of error of plus or minus 3.5 percentage points, the race remains a dead heat.

Supporters want to add language into the state constitutional amendment to define marriage as a union between a man and a woman. Minnesota law already forbids same-sex marriage, but supporters worry that judges or future legislators could change that.

So far, Minnesota for Marriage, the group pushing the amendment, has focused its campaign in churches, through phone banks and the Internet.

Similar marriage amendments have passed in 30 other states.