A proposed constitutional amendment in Minnesota which would define marriage as a heterosexual union is losing support just 12 days before voters head to the polls.

A St. Cloud State University Survey released Thursday found 51 percent of likely voters opposed to the amendment and 44 percent in support.

It is the latest poll to show opponents of marriage equality losing, and the first to be conducted since supporters of the amendment unleashed a barrage of radio and television ads calling on voters to support the amendment.

The Star Tribune Minnesota Poll of likely voters released in September found 49 percent support for the ban and 47 percent against. That marks a 2 percent drop in support from a poll conducted in August.

A further decline was recorded in a Public Policy Polling (PPP) survey released earlier this month. That poll of 937 likely Minnesota voters found support had deteriorated to 46 percent, while 49 percent of respondents said they were opposed.

The latest poll is the first to show a narrow majority opposed to the ban. The Minnesota Post praised the St. Cloud poll for using “gold-standard methodologies.”

In reporting its findings, Star Tribune political editor Patricia Lopez noted that the amendment needs a majority to pass.

“There's an interesting wrinkle in Minnesota's law. It says that you have to have 50 percent of all the ballots cast in the election. So, not just people voting on this amendment, but people voting on everything in November. And that means that if they come up with 49 percent on election day, they'll still lose,” Lopez said.